Diffuse-coloring system and method for a graphics processing framework embodied on a single semiconductor platform

ABSTRACT

A graphics pipeline system is provided for graphics processing. Such system includes a transform module adapted for being coupled to a vertex attribute buffer for receiving vertex data. The transform module serves to transform the vertex data from object space to screen space. Coupled to the transform module is a lighting module which is positioned on the single semiconductor platform for performing lighting operations on the vertex data received from the transform module. Also included is a rasterizer coupled to the lighting module and positioned on the single semiconductor platform for rendering the vertex data received from the lighting module.

RELATED APPLICATIONS

[0001] The present application is related to applications entitled“Method, Apparatus and Article of Manufacture for Area Rasterizationusing Sense Points” which was filed under attorney docket numberNVIDP005, “Method, Apparatus and Article of Manufacture forBoustrophedonic Rasterization” which was filed under attorney docketnumber NVIDP006, “Method, Apparatus and Article of Manufacture forClip-less Rasterization using Line Equation-based Traversal” which wasfiled under attorney docket number NVIDP007, “Method, Apparatus andArticle of Manufacture for a Vertex Attribute Buffer in a GraphicsProcessor” which was filed under attorney docket number NVIDP009,“Method, Apparatus and Article of Manufacture for a Transform Module ina Graphics Processor” which was filed under attorney docket numberNVIDP010, “Method and Apparatus for a Lighting Module in a GraphicsProcessor” which was filed under attorney docket number NVIDP011, and“Method, Apparatus and Article of Manufacture for a Sequencer in aTransform/Lighting Module Capable of Processing Multiple IndependentExecution Threads” which was filed under attorney docket number NVIDP012which were filed concurrently herewith, and which are all incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

[0002] The present invention relates generally to graphics processorsand, more particularly, to graphics pipeline systems includingtransform, lighting and rasterization modules.

BACKGROUND OF THE INVENTION

[0003] Three dimensional graphics are central to many applications. Forexample, computer aided design (CAD) has spurred growth in manyindustries where computer terminals, cursors, CRT's and graphicsterminals are replacing pencil and paper, and computer disks and tapesare replacing drawing vaults. Most, if not all, of these industries havea great need to manipulate and display three-dimensional objects. Thishas lead to widespread interest and research into methods of modeling,rendering, and displaying three-dimensional objects on a computer screenor other display device. The amount of computations needed torealistically render and display a three-dimensional graphical object,however, remains quite large and true realistic display ofthree-dimensional objects have largely been limited to high end systems.There is, however, an ever-increasing need for inexpensive systems thatcan quickly and realistically render and display three dimensionalobjects.

[0004] One industry that has seen a tremendous amount of growth in thelast few years is the computer game industry. The current generation ofcomputer games is moving to three-dimensional graphics in an everincreasing fashion. At the same time, the speed of play is being drivenfaster and faster. This combination has fueled a genuine need for therapid rendering of three-dimensional graphics in relatively inexpensivesystems. In addition to gaming, this need is also fueled by e-Commerceapplications, which demand increased multimedia capabilities.

[0005] Rendering and displaying three-dimensional graphics typicallyinvolves many calculations and computations. For example, to render athree dimensional object, a set of coordinate points or vertices thatdefine the object to be rendered must be formed. Vertices can be joinedto form polygons that define the surface of the object to be renderedand displayed. Once the vertices that define an object are formed, thevertices must be transformed from an object or model frame of referenceto a world frame of reference and finally to two-dimensional coordinatesthat can be displayed on a flat display device. Along the way, verticesmay be rotated, scaled, eliminated or clipped because they fall outsidethe viewable area, lit by various lighting schemes, colorized, and soforth. Thus the process of rendering and displaying a three-dimensionalobject can be computationally intensive and may involve a large numberof vertices.

[0006] A general system that implements such a pipelined system isillustrated in Prior Art FIG. 1. In this system, data source 10generates a stream of expanded vertices defining primitives. Thesevertices are passed one at a time, through pipelined graphic system 12via vertex memory 13 for storage purposes. Once the expanded verticesare received from the vertex memory 13 into the pipelined graphic system12, the vertices are transformed and lit by a transformation module 14and a lighting module 16, respectively, and further clipped and set-upfor rendering by a rasterizer 18, thus generating rendered primitivesthat are displayed on display device 20.

[0007] During operation, the transform module 14 may be used to performscaling, rotation, and projection of a set of three dimensional verticesfrom their local or model coordinates to the two dimensional window thatwill be used to display the rendered object. The lighting module 16 setsthe color and appearance of a vertex based on various lighting schemes,light locations, ambient light levels, materials, and so forth. Therasterization module 18 rasterizes or renders vertices that havepreviously been transformed and/or lit. The rasterization module 18renders the object to a rendering target which can be a display deviceor intermediate hardware or software structure that in turn moves therendered data to a display device.

[0008] When manufacturing graphics processing systems, there is ageneral need to increase the speed of the various graphics processingcomponents, while minimizing costs. In general, integration is oftenemployed to increase the speed of a system. Integration refers to theincorporation of different processing modules on a single integratedcircuit. With such processing modules communicating in a microscopicsemiconductor environment, as opposed to external buses, speed is vastlyincreased.

[0009] Integration if often limited, however, by a cost of implementingand manufacturing multiple processing modules on a single chip. In therealm of graphics processing, any attempt to integrate the transform,lighting, and rasterization modules for increased speed would be costprohibitive. The reason for this increase in cost is that the requiredintegrated circuit would be of a size that is simply too expensive to befeasible.

[0010] This size increase is due mainly to the complexity of the variousengines. High performance transform and lighting engines alone are veryintricate and are thus expensive to implement on-chip, let aloneimplement with any additional functionality. Further, conventionalrasterizers are multifaceted with the tasks of clipping, rendering, etc.making any cost-effective attempt to combine such module with thetransform and lighting modules nearly impossible.

[0011] There is therefore a need for a transform, lighting, andrasterization module having a design that allows cost-effectiveintegration.

DISCLOSURE OF THE INVENTION

[0012] A graphics pipeline system is provided for graphics processing.Such system includes a transform module adapted for being coupled to avertex attribute buffer for receiving vertex data. The transform moduleserves to transform the vertex data from object space to screen space.Coupled to the transform module is a lighting module which is positionedon the single semiconductor platform for performing lighting operationson the vertex data received from the transform module. Also included isa rasterizer coupled to the lighting module and positioned on the singlesemiconductor platform for rendering the vertex data received from thelighting module.

[0013] In one aspect of the present invention, the transform module isdesigned to facilitate integration by including an input buffer adaptedfor being coupled to a vertex attribute buffer for receiving vertex datatherefrom. A multiplication logic unit has a first input coupled to anoutput of the input buffer. Also provided is an arithmetic logic unithaving a first input coupled to an output of the multiplication logicunit. Coupled to an output of the arithmetic logic unit is an input of aregister unit.

[0014] An inverse logic unit is also provided including an input coupledto the output of the arithmetic logic unit for performing an inverse oran inverse square root operation. Further included is a conversionmodule coupled between an output of the inverse logic unit and a secondinput of the multiplication logic unit. In use, the conversion moduleserves to convert scalar vertex data to vector vertex data.

[0015] Memory is coupled to the multiplication logic unit and thearithmetic logic unit. The memory has stored therein a plurality ofconstants and variables for being used in conjunction with the inputbuffer, the multiplication logic unit, the arithmetic logic unit, theregister unit, the inverse logic unit, and the conversion module forprocessing the vertex data. Finally, an output converter is coupled tothe output of the arithmetic logic unit for being coupled to thelighting module to output the processed vertex data thereto.

[0016] To further assist integration, the lighting module includes aplurality of input buffers adapted for being coupled to a transformsystem for receiving vertex data therefrom. The input buffers include afirst input buffer, a second input buffer, and a third input buffer. Aninput of the first buffer, the second input buffer, and the third inputbuffer are coupled to an output of the transform system.

[0017] Further included is a multiplication logic unit having a firstinput coupled to an output of the first input buffer and a second inputcoupled to an output of the second input buffer. An arithmetic logicunit has a first input coupled to an output of the second input buffer.The arithmetic logic unit further has a second input coupled to anoutput of the multiplication logic unit. An output of the arithmeticlogic unit is coupled to the output of the lighting system.

[0018] Next provided is a first register unit having an input coupled tothe output of the arithmetic logic unit and an output coupled to thefirst input of the arithmetic logic unit. A second register unit has aninput coupled to the output of the arithmetic logic unit. Also, suchsecond register has an output coupled to the first input and the secondinput of the multiplication logic unit. A lighting logic unit is alsoprovided having a first input coupled to the output of the arithmeticlogic unit, a second input coupled to the output of the first inputbuffer, and an output coupled to the first input of the multiplicationlogic unit.

[0019] Similar to the transform module, memory is coupled to at leastone of the inputs of the multiplication logic unit and the output of thearithmetic logic unit. The memory has stored therein a plurality ofconstants and variables for being used in conjunction with the inputbuffers, the multiplication logic unit, the arithmetic logic unit, thefirst register unit, the second register unit, and the lighting logicunit for processing the vertex data.

[0020] Together, the foregoing transform/lighting architecture may workwith a rasterizer that operates in homogeneous clip space to provideclip-less rasterization. This facilitates the placement of all of thecomponents on the single semiconductor platform. In order to operate inhomogeneous clip space, the rasterizer determines line equations forlines that define a primitive upon receipt of the primitive from anadjoining set-up module. Thereafter, a W-value is calculated using theline equations for points of intersections of the lines. An area is thendetermined based on the calculated W-values. Such area is representativeof a portion of a display to be depicted. A space in the area is thenidentified using the line equations for rendering pixels therein.

[0021] These and other advantages of the present invention will becomeapparent upon reading the following detailed description and studyingthe various figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The foregoing and other aspects and advantages are betterunderstood from the following detailed description of a preferredembodiment of the invention with reference to the drawings, in which:

[0023]FIG. 1 illustrates a prior art method of rasterization;

[0024]FIG. 1A illustrates the association of a set of edge variableswith a particular pixel in accordance with a prior art method ofrasterization;

[0025]FIG. 1B is a flow diagram illustrating the various components ofone embodiment of the present invention implemented on a singlesemiconductor platform;

[0026]FIG. 2 is a schematic diagram of a vertex attribute buffer (VAB)in accordance with one embodiment of the present invention;

[0027]FIG. 2A is a chart illustrating the various commands that may bereceived by VAB in accordance with one embodiment of the presentinvention;

[0028]FIG. 2B is a flow chart illustrating a method of loading anddraining vertex attributes to and from VAB in accordance with oneembodiment of the present invention;

[0029]FIG. 2C is a schematic diagram illustrating the architecture ofthe present invention employed to implement the operations of FIG. 2B;

[0030]FIG. 3 illustrates the mode bits associated with VAB in accordancewith one embodiment of the present invention;

[0031]FIG. 4 illustrates the transform module of the present invention;

[0032]FIG. 4A is a flow chart illustrating a method of running multipleexecution threads in accordance with one embodiment of the presentinvention;

[0033]FIG. 4B is a flow diagram illustrating a manner in which themethod of FIG. 4A is carried out in accordance with one embodiment ofthe present invention;

[0034]FIG. 5 illustrates the functional units of the transform module ofFIG. 4 in accordance with one embodiment of the present invention;

[0035]FIG. 6 is a schematic diagram of the multiplication logic unit(MLU) of the transform module of FIG. 5;

[0036]FIG. 7 is a schematic diagram of the arithmetic logic unit (ALU)of the transform module of FIG. 5;

[0037]FIG. 8 is a schematic diagram of the register file of thetransform module of FIG. 5;

[0038]FIG. 9 is a schematic diagram of the inverse logic unit (ILU) ofthe transform module of FIG. 5;

[0039]FIG. 10 is a chart of the output addresses of output converter ofthe transform module of FIG. 5 in accordance with one embodiment of thepresent invention;

[0040]FIG. 11 is an illustration of the micro-code organization of thetransform module of FIG. 5 in accordance with one embodiment of thepresent invention;

[0041]FIG. 12 is a schematic diagram of the sequencer of the transformmodule of FIG. 5 in accordance with one embodiment of the presentinvention;

[0042]FIG. 13 is a flowchart delineating the various operationsassociated with use of the sequencer of the transform module of FIG. 12;

[0043]FIG. 14 is a flow diagram delineating the operation of thesequencing component of the sequencer of the transform module of FIG.12;

[0044]FIG. 14A is a flow diagram illustrating the components of thepresent invention employed for handling scalar and vector componentsduring graphics-processing;

[0045]FIG. 14B is a flow diagram illustrating one possible combination1451 of the functional components of the present invention shown in FIG.14A which corresponds to the transform module of FIG. 5;

[0046]FIG. 14C is a flow diagram illustrating another possiblecombination 1453 of the functional components of the present inventionshown in FIG. 14A;

[0047]FIG. 14D illustrates a method implemented by the transform moduleof FIG. 12 for performing a blending operation duringgraphics-processing in accordance with one embodiment of the presentinvention;

[0048]FIG. 15 is a schematic diagram of the lighting module of oneembodiment of the present invention;

[0049]FIG. 16 is a schematic diagram showing the functional units of thelighting module of FIG. 15 in accordance with one embodiment of thepresent invention;

[0050]FIG. 17 is a schematic diagram of the multiplication logic unit(MLU) of the lighting module of FIG. 16 in accordance with oneembodiment of the present invention;

[0051]FIG. 18 is a schematic diagram of the arithmetic logic unit (ALU)of the lighting module of FIG. 16 in accordance with one embodiment ofthe present invention;

[0052]FIG. 19 is a schematic diagram of the register unit of thelighting module of FIG. 16 in accordance with one embodiment of thepresent invention;

[0053]FIG. 20 is a schematic diagram of the lighting logic unit (LLU) ofthe lighting module of FIG. 16 in accordance with one embodiment of thepresent invention;

[0054]FIG. 21 is an illustration of the flag register associated withthe lighting module of FIG. 16 in accordance with one embodiment of thepresent invention;

[0055]FIG. 22 is an illustration of the micro-code fields associatedwith the lighting module of FIG. 16 in accordance with one embodiment ofthe present invention;

[0056]FIG. 23 is a schematic diagram of the sequencer associated withthe lighting module of FIG. 16 in accordance with one embodiment of thepresent invention;

[0057]FIG. 24 is a flowchart delineating the manner in which thesequencers of the transform and lighting modules are capable ofcontrolling the input and output of the associated buffers in accordancewith one embodiment of the present invention;

[0058]FIG. 25 is a diagram illustrating the manner in which thesequencers of the transform and lighting modules are capable ofcontrolling the input and output of the associated buffers in accordancewith the method of FIG. 24;

[0059]FIG. 25B is a schematic diagram of the various modules of therasterizer of FIG. 1B;

[0060]FIG. 26 illustrates a schematic of the set-up module of therasterization module of the present invention;

[0061]FIG. 26A is an illustration showing the various parameterscalculated by the set-up module of the rasterizer of FIG. 26;

[0062]FIG. 27 is a flowchart illustrating a method of the presentinvention associated with the set-up and traversal modules of therasterizer component shown in FIG. 26;

[0063]FIG. 27A illustrates sense points that enclose a convex regionthat is moved to identify an area in a primitive in accordance with oneembodiment of the present invention;

[0064]FIG. 28 is a flowchart illustrating a process of the presentinvention associated with the process row operation 2706 of FIG. 27;

[0065]FIG. 28A is an illustration of the sequence in which the convexregion of the present invention is moved about the primitive;

[0066]FIG. 28B illustrates another example of the sequence in which theconvex region of the present invention is moved about the primitive;

[0067]FIG. 29 is a flowchart illustrating an alternate boustrophedonicprocess of the present invention associated with the process rowoperation 2706 of FIG. 27;

[0068]FIG. 29A is an illustration of the sequence in which the convexregion of the present invention is moved about the primitive inaccordance with the boustrophedonic process of FIG. 29;

[0069]FIG. 30 is a flowchart illustrating an alternate boustrophedonicprocess using boundaries;

[0070]FIG. 31 is a flowchart showing the process associated withoperation 3006 of FIG. 30;

[0071]FIG. 31A is an illustration of the sequence in which the convexregion of the present invention is moved about the primitive inaccordance with the boundary-based boustrophedonic process of FIGS. 30and 31;

[0072]FIG. 32 is a flowchart showing the process associated withoperation 2702 of FIG. 27;

[0073]FIG. 32A is an illustration showing which area is drawn if nonegative W-values are calculated in the process of FIG. 32;

[0074]FIG. 32B is an illustration showing which area is drawn if onlyone negative W-value is calculated in the process of FIG. 32; and

[0075]FIG. 32C is an illustration showing which area is drawn if onlytwo negative W-values are calculated in the process of FIG. 32.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0076]FIGS. 1 and 1A show the prior art. FIGS. 1B-32C show a graphicspipeline system of the present invention.

[0077]FIG. 1B is a flow diagram illustrating the various components ofone embodiment of the present invention. As shown, the present inventionis divided into four main modules including a vertex attribute buffer(VAB) 50, a transform module 52, a lighting module 54, and arasterization module 56 with a set-up module 57. In one embodiment, eachof the foregoing modules is situated on a single semiconductor platformin a manner that will be described hereinafter in greater detail. In thepresent description, the single semiconductor platform may refer to asole unitary semiconductor-based integrated circuit or chip.

[0078] The VAB 50 is included for gathering and maintaining a pluralityof vertex attribute states such as position, normal, colors, texturecoordinates, etc. Completed vertices are processed by the transformmodule 52 and then sent to the lighting module 54. The transform module52 generates vectors for the lighting module 54 to light. The output ofthe lighting module 54 is screen space data suitable for the set-upmodule which, in turn, sets up primitives. Thereafter, rasterizationmodule 56 carries out rasterization of the primitives. It should benoted that the transform and lighting modules 52 and 54 might only stallon the command level such that a command is always finished oncestarted.

[0079] In one embodiment, the present invention includes a hardwareimplementation that at least partially employs Open Graphics Library(OpenGL®) and D3D™ transform and lighting pipelines. OpenGL® is thecomputer industry's standard application program interface (API) fordefining 2-D and 3-D graphic images. With OpenGL®, an application cancreate the same effects in any operating system using anyOpenGL®-adhering graphics adapter. OpenGL® specifies a set of commandsor immediately executed functions. Each command directs a drawing actionor causes special effects.

[0080]FIG. 2 is a schematic diagram of VAB 50 in accordance with oneembodiment of the present invention. As shown, VAB 50 passes commandbits 200 while storing data bits 204 representative of attributes of avertex and mode bits 202. In use VAB 50 receives the data bits 204 ofvertices and drains the same.

[0081] The VAB 50 is adapted for receiving and storing a plurality ofpossible vertex attribute states via the data bits 204. In use aftersuch data bits 204, or vertex data, is received and stored in VAB 50,the vertex data is outputted from VAB 50 to a graphics-processingmodule, namely the transform module 52. Further, the command bits 200are passed by VAB 50 for determining a manner in which the vertex datais inputted to VAB 50 in addition to other processing which will bedescribed in greater detail with reference to FIG. 2A. Such command bits200 are received from a command bit source such as a microcontroller,CPU, data source or any other type of source which is capable ofgenerating command bits 200.

[0082] Further, mode bits 202 are passed which are indicative of thestatus of a plurality of modes of process operations. As such, mode bits202 are adapted for determining a manner in which the vertex data isprocessed in the subsequent graphics-processing modules. Such mode bits202 are received from a command bit source such as a microcontroller,CPU, data source or any other type of source which is capable ofgenerating mode bits 202.

[0083] It should be noted that the various functions associated with VAB50 may be governed by way of dedicated hardware, software or any othertype of logic. In various embodiments, 64, 128, 256 or any other numberof mode bits 202 may be employed.

[0084] The VAB 50 also functions as a gathering point for the 64 bitdata that needs to be converted into a 128-bit format. The VAB 50 inputis 64 bits/cycle and the output is 128 bits/cycle. In other embodiments,VAB 50 may function as a gathering point for 128-bit data, and VAB 50input maybe 128 bits/cycle or any other combination. The VAB 50 furtherhas reserved slots for a plurality of vertex attributes that are allIEEE 32 bit floats. The number of such slots may vary per the desires ofthe user. Table 1 illustrates exemplary vertex attributes employed bythe present invention. TABLE 1 Postion: x,y,z,w Diffuse Color: r,g,b,aSpecular Color: r,g,b Fog: f Texture0: s,t,r,q Texture1: s,t,r,q Normal:nx,ny,nz Skin Weight: w

[0085] During operation, VAB 50 may operate assuming that the x,y datapair is written before the z,w data pair since this allows fordefaulting the z,w pair to (0.0,1.0) at the time of the x,y write. Thismay be important for default components in OpenGL® and D3D™. It shouldbe noted that the position, texture0, and texture1 slots default thethird and fourth components to (0.0,1.0). Further, the diffuse colorslot defaults the fourth component to (1.0) and the texture slotsdefault the second component to (0.0).

[0086] The VAB 50 includes still another slot 205 used for assemblingthe data bits 204 that may be passed into or through the transform andlighting module 52 and 54, respectively, without disturbing the databits 204. The data bits 204 in the slot 205 can be in a floating pointor integer format. As mentioned earlier, the data bits 204 of eachvertex has an associated set of mode bits 202 representative of themodes affecting the processing of the data bits 204. These mode bits 202are passed with the data bits 204 through the transform and lightingmodules 52 and 54, respectively, for purposes that will be set forthhereinafter in greater detail.

[0087] In one embodiment, there may be 18 valid VAB, transform, andlighting commands received by VAB 50. FIG. 2A is a chart illustratingthe various commands that may be received by VAB 50 in accordance withone embodiment of the present invention. It should be understood thatall load and read context commands, and the passthrough command shown inthe chart of FIG. 2A transfer one data word of up to 128 bits or anyother size.

[0088] Each command of FIG. 2A may contain control information dictatingwhether each set of data bits 204 is to be written into a high doubleword or low double word of one VAB address. In addition, a 2-bit writemask may be employed for providing control to the word level. Further,there may be a launch bit that informs VAB controller that all of thedata bits 204 are present for a current command to be executed.

[0089] Each command has an associated stall field that allows a look-upto find information on whether the command is a read command in that itreads context memory or is a write command in that it writes contextmemory. By using the stall field of currently executing commands, thenew command may be either held off in case of conflict or allowed toproceed.

[0090] In operation, VAB 50 can accept one input data word up to 128bits (or any other size) per cycle and output one data word up to 128bits (or any other size) per cycle. For the load commands, this meansthat it may take two cycles to load the data into VAB 50 to create a128-bit quad-word and one cycle to drain it. For the scalar memories inthe lighting module 54, it is not necessary to accumulate a fullquad-word, and these can be loaded in one cycle/address. For one vertex,it can take up to 14 acycles to load the 7 VAB slots while it only takes7 cycles to drain them. It should be noted, however, that it is onlynecessary to update the vertex state that changes between executingvertex commands. This means that, in one case, the vertex position maybe updated taking 2 cycles, while the draining of the vertex data takes7 cycles. It should be noted that only 1 cycle may be required in thecase of the x,y position.

[0091]FIG. 2B is a flow chart illustrating one method of loading anddraining vertex attributes to and from VAB 50 duringgraphics-processing. Initially, in operation 210, at least one set ofvertex attributes is received in VAB 50 for being processed. Asmentioned earlier, each set of vertex attributes may be unique, andcorrespond to a single vertex.

[0092] In use the vertex attributes are stored in VAB 50 upon thereceipt thereof in operation 212. Further, each set of stored vertexattributes is transferred to a corresponding one of a plurality of inputbuffers of the transform module 52. The received set of vertexattributes is also monitored in order to determine whether a receivedvertex attribute has a corresponding vertex attribute of a different setcurrently stored in VAB 50, as indicated in operation 216.

[0093] Upon it being determined that a stored vertex attributecorresponds to the received vertex attribute in decision 217, the storedvertex attribute is outputted to the corresponding input buffer of thetransform module 52 out of order. See operation 218. Immediately uponthe stored vertex attribute being outputted, the corresponding incomingvertex attribute may take its place in VAB 50. If no correspondence isfound, however, each set of the stored vertex attributes may betransferred to the corresponding input buffer of the transform module 52in accordance with a regular predetermined sequence. Note operation 219.

[0094] It should be noted that the stored vertex attribute might not betransferred in the aforementioned manner if it has an associated launchcommand. Further, in order for the foregoing method to work properly,the bandwidth of an output of VAB 50 must be at least the bandwidth ofan input of VAB 50.

[0095]FIG. 2C is a schematic diagram illustrating the architecture ofthe present invention employed to implement the operations of FIG. 2B.As shown, VAB 50 has a write data terminal WD, a read data terminal RD,a write address terminal WA, and a read address RA terminal. The readdata terminal is coupled to a first clock-controlled buffer 230 foroutputting the data bits 204 from VAB 50.

[0096] Also included is a first multiplexer 232 having an output coupledto the read address terminal of VAB 50 and a second clock-controlledbuffer 234. A first input of the first multiplexer 232 is coupled to thewrite address terminal of VAB 50 while a second input of the firstmultiplexer 232 is coupled to an output of a second multiplexer 236. Alogic module 238 is coupled between the first and second multiplexers232 and 236, the write address terminal of VAB 50, and an output of thesecond clock-controlled buffer 234.

[0097] In use the logic module 238 serves to determine whether anincoming vertex attribute is pending to drain in VAB 50. In oneembodiment, this determination may be facilitated by monitoring a bitregister that indicates whether a vertex attribute is pending or not. Ifit is determined that the incoming vertex attribute does have a matchcurrently in VAB 50, the logic module 238 controls the first multiplexer232 in order to drain the matching vertex attribute so that the incomingvertex attribute may be immediately stored in its place. On the otherhand, if it is determined that the incoming vertex attribute does nothave a match currently in VAB 50, the logic module 238 controls thefirst multiplexer 232 such that VAB 50 is drained and the incomingvertex attribute is loaded sequentially or in some other predeterminedorder, per the input of the second multiplexer 236 which may be updatedby the logic module 238.

[0098] As a result, there is no requirement for VAB 50 to drain multiplevertex attributes before a new incoming vertex attribute may be loaded.The pending vertex attribute forces out the corresponding VABcounterpart if possible, thus allowing it to proceed. As a result, VAB50 can drain in an arbitrary order. Without this capability, it wouldtake 7 cycles to drain VAB 50 and possibly 14 more cycles to load it. Byoverlapping the loading and draining, higher performance is achieved. Itshould be noted that this is only possible if an input buffer is emptyand VAB 50 can drain into input buffers of the transform module 52.

[0099]FIG. 3 illustrates the mode bits associated with VAB 50 inaccordance with one embodiment of the present invention. Thetransform/light mode information is stored in a register via mode bits202. Mode bits 202 are used to drive the sequencers of the transformmodule 52 and lighting module 54 in a manner that will be becomeapparent hereinafter. Each vertex has associated mode bits 202 that maybe unique, and can therefore execute a specifically tailored programsequence. While, mode bits 202 may generally map directly to thegraphics API, some of them may be derived.

[0100] In one embodiment, the active light bits (LIS) of FIG. 3 may becontiguous. Further, the pass-through bit (VPAS) is unique in that whenit is turned on, the vertex data is passed through with scale and bias,and no transforms or lighting is done. Possible mode bits 202 used whenVPAS is true are the texture divide bits (TDV0,1), and foggen bits (usedto extract fog value in D3D™). VPAS is thus used for pre-transformeddata, and TDV0,1 are used to deal with a cylindrical wrap mode in thecontext of D3D™.

[0101]FIG. 4 illustrates the transform module of one embodiment of thepresent invention. As shown, the transform module 52 is connected to VAB50 by way of 6 input buffers 400. In one embodiment, each input buffer400 might be 7*128b in size. The 6 input buffers 400 each is capable ofstoring 7 quad words. Such input buffers 400 follow the same layout asVAB 50, except that the pass data is overlapped with the position data.

[0102] In one embodiment, a bit might be designated for each attributeof each input buffer 400 to indicate whether data has changed since theprevious instance that the input buffer 400 was loaded. By this design,each input buffer 400 might be loaded only with changed data.

[0103] The transform module 52 is further connected to 6 output vertexbuffers 402 in the lighting module 54. The output buffers include afirst buffer 404, a second buffer 406, and a third buffer 408. As willbecome apparent hereinafter, the contents, i.e. position, texturecoordinate data, etc., of the third buffer 408 are not used in thelighting module 54. The first buffer 404 and second buffer 406 are both,however, used for inputting lighting and color data to the lightingmodule 54. Two buffers are employed since the lighting module is adaptedto handle two read inputs. It should be noted that the data might bearranged so as to avoid any problems with read conflicts, etc.

[0104] Further coupled to the transform module 52 is context memory 410and micro-code ROM memory 412. The transform module 52 serves to convertobject space vertex data into screen space, and to generate any vectorsrequired by the lighting module 54. The transform module 52 also doesprocesses skinning and texture coordinates. In one embodiment, thetransform module 52 might be a 128-bit design processing 4 floats inparallel, and might be optimized for doing 4 term dot products.

[0105]FIG. 4A is a flow chart illustrating a method of executingmultiple threads in the transform module 52 in accordance with oneembodiment of the present invention. In operation, the transform module52 is capable of processing 3 vertices in parallel via interleaving. Tothis end, 3 commands can be simultaneously executed in parallel unlessthere are stall conditions between the commands such as writing andsubsequently reading from the context memory 410. The 3 executionthreads are independent of each other and can be any command since allvertices contain unique corresponding mode bits 202.

[0106] As shown in FIG. 4A, the method of executing multiple threadsincludes determining a current thread to be executed in operation 420.This determination might be made by identifying a number of cycles thata graphics-processing module requires for completion of an operation,and tracking the cycles. By tracking the cycles, each thread can beassigned to a cycle, thus allowing determination of the current threadbased on the current cycle. It should be noted, however, that suchdetermination might be made in any desired manner that is deemedeffective.

[0107] Next, in operation 422, an instruction associated with a threadto be executed during a current cycle is retrieved using a correspondingprogram counter number. Thereafter, the instruction is executed on thegraphics-processing module in operation 424.

[0108] In one example of use, the instant method includes firstaccessing a first instruction, or code segment, per a first programcounter. As mentioned earlier, such program counter is associated with afirst execution thread. Next, the first code segment is executed in thegraphics-processing module. As will soon become apparent, suchgraphics-processing module might take the form of an adder, amultiplier, or any other functional unit or combination thereof.

[0109] Since the graphics-processing module requires more than one clockcycle to complete the execution, a second code segment might be accessedper a second program counter immediately one clock cycle after theexecution of the first code segment. The second program counter isassociated with a second execution thread, wherein each of the executionthreads process a unique vertex.

[0110] To this end, the second code segment might begin execution in thegraphics-processing module prior to the completion of the execution ofthe first code segment in the graphics-processing module. In use thegraphics-processing module requires a predetermined number of cycles forevery thread to generate an output. Thus, the various steps of thepresent example might be repeated for every predetermined number ofcycles.

[0111] This technique offers numerous advantages over the prior art. Ofcourse, the functional units of the present invention are used moreefficiently. Further, the governing code might be written moreefficiently when the multiple threading scheme is assumed to be used.

[0112] For example, in the case where the graphics-processing moduleincludes a multiplier that requires three clock cycles to output ananswer, it would be necessary to include two no operation commandsbetween subsequent operations such as a=b*c and d=e*a, since “a” wouldnot be available until after the three clock cycles. In the presentembodiment, however, the code might simply call d=e*a immediatelysubsequent a=b*c, because it can be assumed that such code will beexecuted as one of three execution threads that are called once everythree clock cycles.

[0113]FIG. 4B is a flow diagram illustrating a manner in which themethod of FIG. 4A is carried out. As shown, each execution thread has anassociated program counter 450 that is used to access instructions, orcode segments, in instruction memory 452. Such instructions might thenbe used to operate a graphics-processing module such as an adder 456, amultiplier 454, and/or an inverse logic unit or register 459.

[0114] In order to accommodate a situation where at least two of theforegoing processing modules are used in tandem, at least one codesegment delay 457 is employed between the graphics-processing modules.In the case where a three-thread framework is employed, a three-clockcycle code segment delay 457 is used. In one embodiment, the codesegment delay 457 is used when a multiplication instruction is followedby an addition instruction. In such case, the addition instruction isnot executed until three clock cycles after the execution of themultiplication instruction in order to ensure that time has elapsedwhich is sufficient for the multiplier 456 to generate an output.

[0115] After the execution of each instruction, the program counter 450of the current execution thread is updated and the program counter ofthe next execution thread is called by module 458 in a round robinsequence to access an associated instruction. It should be noted thatthe program counters might be used in any fashion including, but notlimited to incrementing, jumping, calling and returning, performing atable jump, and/or dispatching. Dispatching refers to determining astarting point of code segment execution based on a received parameter.Further, it important to understand that the principles associated withthe present multiple thread execution framework might also be applied tothe lighting module 54 of the graphics-processing pipeline of thepresent invention.

[0116] In the case where a three-thread framework is employed, eachthread is allocated one input buffer and one output buffer at any onetime. This allows loading of three more commands with data whileprocessing three commands. The input buffers and output buffers areassigned in a round robin sequence in a manner that will be discussedlater with reference to FIGS. 27 and 28.

[0117] The execution threads are thus temporally and functionallyinterleaved. This means that each function unit is pipelined into threestages and each thread occupies one stage at any one time. In oneembodiment, the three-threads might be set to always execute in the samesequence, i.e. zero then one then three. Conceptually, the threads entera function unit at t=clock modulo three. Once a function unit startswork, it takes three cycles to deliver the result (except the ILU thattakes six), at which time the same thread is again active.

[0118]FIG. 5 illustrates the functional units of the transform module 52of FIG. 4 in accordance with one embodiment of the present invention. Asshown, included are input buffers 400 that are adapted for being coupledto VAB 50 for receiving vertex data therefrom.

[0119] A memory logic unit (MLU) 500 has a first input coupled to anoutput of input buffers 400. As an option, the output of MLU 500 mighthave a feedback loop 502 coupled to the first input thereof.

[0120] Also provided is an arithmetic logic unit (ALU) 504 having afirst input coupled to an output of MLU 500. The output of ALU 504further has a feedback loop 506 connected to the second input thereof.Such feedback loop 502 may further have a delay 508 coupled thereto.Coupled to an output of ALU 504 is an input of a register unit 510. Itshould be noted that the output of register unit 510 is coupled to thefirst and second inputs of MLU 500.

[0121] An inverse logic unit (ILU) 512 is provided including an inputcoupled to the output of ALU 504 for performing an inverse or an inversesquare root operation. In an alternate embodiment, ILU 512 might includean input coupled to the output of register unit 510.

[0122] Further included is a conversion, or smearing, module 514 coupledbetween an output of ELU 512 and a second input of MLU 500. In use theconversion module 514 serves to convert scalar vertex data to vectorvertex data. This is accomplished by multiplying the scalar data by avector so that the vector operators such as the multiplier and/or addermay process it. For example, a scalar A, after conversion, may become avector (A,A,A,A). In an alternate embodiment, the smearing module 514might be incorporated into the multiplexers associated with MLU 500, orany other component of the present invention. As an option, a register516 might be coupled between the output of ILU 512 and an input of theconversion unit 514. Further, such register 516 might be threaded.

[0123] Memory 410 is coupled to the second input of MLU 500 and theoutput of ALU 504. In particular, memory 410 has a read terminal coupledto the second input of MLU 500. Further, memory 410 has a write terminalcoupled to the output of ALU 504.

[0124] The memory 410 has stored therein a plurality of constants andvariables for being used in conjunction with the input buffer 400, MLU500, ALU 504, register unit 510, ILU 512, and the conversion module 514for processing the vertex data. Such processing might includetransforming object space vertex data into screen space vertex data,generating vectors, etc.

[0125] Finally, an output converter 518 is coupled to the output of ALU504. The output converter 518 serves for being coupled to a lightingmodule 54 via output buffers 402 to output the processed vertex datathereto. All data paths except for the ILU might be designed to be 128bits wide or other data path widths may be used.

[0126]FIG. 6 is a schematic diagram of MLU 500 of the transform module52 of FIG. 5 in accordance with one embodiment of the present invention.As shown, MLU 500 of the transform module 52 includes four multipliers600 that are coupled in parallel.

[0127] MLU 500 of transform module 52 is capable of multiplying two fourcomponent vectors in three different ways, or pass one four componentvector. MLU 500 is capable of performing multiple operations. Table 2illustrates such operations associated with MLU 500 of transform module52. TABLE 2 CMLU_MULT o[0] = a[0]*b[0],o[1] = a [1]*b[1],o[2] = a[2]*b[2],o[3] = a[3]*b[3] CMLU_MULA o[0] = a[0]*b[0],o[1] = a [1]*b[1],o[2]= a[2] *b[2],o[3] = a[3] CMLU_MULB o[0] = a[0]*b[0],o[1] = a[1]*b[1],o[2] = a[2] *b[2],o[3] = b[3] CMLU_PASA o[0] = a[0],o[1] =a[1],o[2] = a[2], o[3] = a[3] CMLU_PASB o[0] = b[0],o[1] = b[1],o[2] =b[2], o[3] = b[3]

[0128] Possible A and B inputs are shown in Table 3. TABLE 3 MA_M MLUMA_V Input Buffer MA_R RLU (shared with MB_R) MB_I ILU MB_C ContextMemory MB_R RLU (shared with MA_R)

[0129] Table 4 illustrates a vector rotate option capable of being usedfor cross products. TABLE 4 MR_NONE No change MR_ALBR Rotate A[XYZ]vector left, B[XYZ] vector right MR_ARBL Rotate A[XYZ] vector right,B[XYZ] vector left

[0130]FIG. 7 is a schematic diagram of ALU 504 of transform module 52 ofFIG. 5 in accordance with one embodiment of the present invention. Asshown, ALU 504 of transform module 52 includes three adders 700 coupledin parallel/series. In use ALU 504 of transform module 52 can add twothree component vectors, pass one four component vector, or smear avector component across the output. Table 5 illustrates variousoperations of which ALU 504 of transform module 52 is capable. TABLE 5CALU_ADDA o[0] = a[0]+b[0],o[1] = a[1]+b[1],o[2] = a[2],o[3] = a[3]CALU_ADDB o[0] = a[0]+b[0],o[1] = a[1]+b[1],o[2] = a[2],o[3] = b[3]CALU_SUM3B o[0123] = b[0] + b[1] + b[2] CALU_SUM4B o[0123] = b[0] +b[1] + b[2] + b[3] CALU_SMRB0 o[0123] = b[0] CALU_SMRB1 o[0123] = b[1]CALU_SMRB2 o[0123] = b[2] CALU_SMRB3 o[0123] = b[3] CALU_PASA o[0] = a[0,o[1] = a[1],o[2] = a[2],o[3] = a[3] CALU_PASB o[0] = b[0 ,o[1] =b[1],o[2] = b[2],o[3] = b[3]

[0131] Table 6 illustrates the A and B inputs of ALU 504 of transformmodule 52. TABLE 6 AA_A ALU (one instruction delay) AA_C Context MemoryAB_M MLU

[0132] It is also possible to modify the sign bits of the A and B inputby effecting no change, negation of B, negation of A, absolute valueA,B. It should be noted that when ALU 504 outputs scalar vertex data,this scalar vertex data is smeared across the output in the sense thateach output represents the scalar vertex data. The pass control signalsof MLU 500 and ALU 504 are each capable of disabling all special valuehandling during operation.

[0133]FIG. 8 is a schematic diagram of the vector register file 510 oftransform module 52 of FIG. 5 in accordance with one embodiment of thepresent invention. As shown, the vector register file 510 includes foursets of registers 800 each having an output connected to a first inputof a corresponding multiplexer 802 and an input coupled to a secondinput of the corresponding multiplexer 802.

[0134] In one embodiment of the present invention, the vector registerfile 510 is threaded. That is, there are three copies of the vectorregister file 510 and each thread has its own copy. In one embodiment,each copy contains eight registers, each of which might be 128 bits insize and store four floats. The vector register file 510 is written fromALU 504 and the output is fed back to MLU 500. The vector register file510 has one write and one read per cycle.

[0135] In operation, it is also possible to individually mask a writeoperation to each register component. The vector register file 510exhibits zero latency when the write address is the same as the readaddress due to a bypass path 511 from the input to the output. In thiscase, unmasked components would be taken from the registers and maskedcomponents would be bypassed. The vector register file 510 is thus veryuseful for building up vectors component by component, or for changingthe order of vector components in conjunction with the ALU SMRoperations (See Table 5). Temporary results might be also stored in thevector register file 510.

[0136]FIG. 9 is a schematic diagram of ILU 512 of transform module 52 ofFIG. 5 in accordance with one embodiment of the present invention. Asshown, ILU 512 of transform module 52 is capable of generating afloating-point reciprocal (1/D) and a reciprocal square root (1/D A(½)).To carry out such operations, either one of two iterative processesmight be executed on a mantissa. Such processes might be executed withany desired dedicated hardware, and are shown below: Reciprocal (1/D)Reciprocal Square-root (1/D^ (1/2)) x_(n)+1 = x_(n)(2-x_(n)*D) x_(n+1) =(1/2)*x_(n)(2-x_(n) ²*D) 1) table look up for x_(n) (seed) table look upfor x_(n) (seed) x_(n) x_(n) * x_(n) 2) 1^(st) iteration: multiply-add1^(st) iteration: multiply-add 2-x_(n)*D 3-x_(n) ²*D 3) 1^(st)iteration: multiply 1^(st) iteration: multiply x_(n)(2-x_(n)*D)(1/2)*x_(n)(3-x_(n) ²*D) 4) 2^(nd) iteration: no-op 2^(nd) iteration:square pass x_(n)+1 x_(n+1) ² 5) 2^(nd) iteration: multiply-add 2^(nd)iteration: multiply-add 2-x_(n+1)*D 3-x_(n+1) ²*D 6) 2^(nd) iteration:multiply 2^(nd) iteration: multiply x_(n+1) (2-x_(n+1)*D)(1/2)*x_(n+1)(3-x_(n+1) ²*D)

[0137] As shown, the two processes are similar, affording astraightforward design. It should be noted that the iterations might berepeated until a threshold precision is met.

[0138] In operation, ILU 512 performs two basic operations including aninverse operation and inverse square root operation. Unlike the otherunits, it requires six cycles to generate the output. The input is ascalar, and so is the output. As set forth earlier, the threaded holdingregister 516 at ELU 512 output is relied upon to latch the result untilthe next time a valid result is generated. Further, the scalar output issmeared into a vector before being fed into MLU 500. The inverse unit512 uses look-up tables and a two pass Newton-Raphson iteration togenerate IEEE (Institute of Electrical and Electronics Engineers)outputs accurate to within about 22 mantissa bits. Table 7 illustratesthe various operations that might be performed by ILU 512 of transformmodule 52. TABLE 7 CILU_INV o = 1.0/a CILU_ISQ o = 1.0/sqrt(a) CILU_CINVo = 1.0/a (with range clamp) CILU_NOP no output

[0139] The foregoing range clamp inversion operation of Table 7 might beused to allow clipping operations to be handled by rasterization module56. Coordinates are transformed directly into screen space that canresult in problems when the homogeneous clip space w is near 0.0. Toavoid multiplying by 1.0/0.0 in the perspective divide, the 1/wcalculation is clamped to a minimum and a maximum exponent.

[0140] In use the context memory 410 as shown in FIG. 5 reads and writesonly using quad-words. The memory can be read by MLU 500 or ALU 504 eachcycle, and can be written by ALU 504. Only one memory read is allowedper cycle. If a read is necessary, it is done at the start of aninstruction and then pipelined down to ALU 504 three cycles later.Context memory 410 need not necessarily be threaded.

[0141]FIG. 10 is a chart of the output addresses of output converter 518of transform module 52 of FIG. 5 in accordance with one embodiment ofthe present invention. The output converter 518 is responsible fordirecting the outputs to proper destinations, changing the bit precisionof data, and some data swizzling to increase performance. All datadestined for lighting module 54 is rounded to a 22 bit floating pointformat organized as S1E8M13 (one sign, eight exponent, 13 mantissabits). The destination buffers 402 as shown in FIG. 4 in lighting module54 are threaded.

[0142] Data swizzling is useful when generating vectors. Such techniqueallows the generation of a distance vector (1,d,d*d) without penaltywhen producing a vector. The distance vector is used for fog, pointparameter and light attenuation. This is done with an eye vector andlight direction vectors. Table 8 illustrates the various operationsassociated with such vectors. It should be noted that, in the followingtable, squaring the vector refers to d²=dot[(x,y,z), (x,y,z)], andstoring d² in the w component of (x,y,z). TABLE 8 1. Square the vector(x,y,z,d*d) (output d*d to VBUF, 1.0 to VBUF) 2. Generate inverse sqrtof d*d (1/d) 3. Normalized vector (x/d,y/d,z/d,d) (output x/d,y/d,z/d toWBUF, d to VBUF)

[0143] It should be noted that the math carried out in the presentinvention might not always be IEEE compliant. For example, it might beassumed that “0” multiplied by any number renders “0.” This isparticularly beneficial when dealing with the equations such asd=d²*1(d²)^(½), where d=0. Without making the foregoing assumption, suchequation would afford an error, thus causing problems in making relatedcomputations.

[0144]FIG. 11 is an illustration of the micro-code organization oftransform module 52 of FIG. 5 in accordance with one embodiment of thepresent invention. The transform module micro-code might be arrangedinto 15 fields making up a total width of 44 bits. Fields might bedelayed to match the data flow of the units. MLU 500 operations areexecuted at a delay of zero, ALU operations are executed at a delay ofone, and RLU, output operations are executed at a delay of two. Eachdelay is equivalent to three cycles.

[0145]FIG. 12 is a schematic diagram of sequencer 1200 of transformmodule 52 of FIG. 5 in accordance with one embodiment of the presentinvention. As shown in FIG. 12, sequencer 1200 of transform module 52includes a buffer 1202 adapted for receiving the mode bits from VAB 50that are indicative of the status of a plurality of modes of processoperations.

[0146] Also included is memory 412 capable of storing code segments thateach are adapted to carry out the process operations in accordance wishthe status of the modes. A sequencing module 1206 is coupled betweenmemory 412 and a control vector module 1205 which is in turn coupled tobuffer 1202 for identifying a plurality of addresses in memory 412 basedon a control vector derived from mode bits 202. The sequencing module1206 is further adapted for accessing the addresses in memory 412 forretrieving the code segments that might be used to operate transformmodule 52 to transfer data to an output buffer 1207.

[0147]FIG. 13 is a flowchart delineating the various operationsassociated with use of sequencer 1200 of transform module 52 of FIG. 12.As shown, sequencer 1200 is adapted for sequencing graphics-processingin a transform or lighting operation. In operation 1320, mode bits 202are first received which are indicative of the status of a plurality ofmodes of process operations. In one embodiment, mode bits 202 might bereceived from a software driver.

[0148] Then, in operation 1322, pluralities of addresses are thenidentified in memory based on mode bits 202. Such addresses are thenaccessed in the memory in operation 1324 for retrieving code segmentsthat each are adapted to carry out the process operations in accordancewith the status of the modes. The code segments are subsequentlyexecuted with a transform or lighting module for processing vertex data.Note operation 1326.

[0149]FIG. 14 is a flow diagram delineating the operation of thesequencing module 1206 of sequencer 1200 of transform module 52 of FIG.12. As shown, a plurality of mode registers 1430 each include a uniqueset of mode bits 202 which in turn correspond to a single vertex. Itshould be noted that mode registers 1430 are polled in a round robinsequence in order to allow the execution of multiple execution threadsin the manner set forth earlier during reference to FIGS. 4A and 4B.

[0150] Once the current execution thread is selected, a correspondinggroup of mode bits 202 are decoded in operation 1432. Upon mode bits 202being decoded in operation 1432, a control vector is afforded whichincludes a plurality of bits each of which indicate whether a particularcode segment is to be accessed in ROM 1404 for processing thecorresponding vertex data.

[0151] Upon determining whether a code segment should be accessed in ROM1404 and executed, a pointer operation 1436 increments the currentthread pointer to start the next execution thread to obtain a secondgroup mode bits 202 to continue a similar operation. This might becontinued for each of the threads in a round robin sequence.

[0152] Once the control vector has been formed for a particular group ofmode bits 202, a priority encoder operation 1438 determines, oridentifies, a next “1” or enabled, bit of the control vector. If such abit is found, the priority encoder operation 1438 produces an address inROM 1404 corresponding to the enabled bit of the control vector forexecution purposes.

[0153] Upon returning to the initial group of mode bits 202 afterhandling the remaining threads, and after the mode bits have beendecoded and the control vector is again available, a masking operation1434 might be used to mask the previous “1”, or enabled, bit that wasidentified earlier. This allows analysis of all remaining bits aftermask operation 1434.

[0154] The foregoing process might be illustrated using the followingtables. Table 9 shows a plurality of equations that might be executed onsubject vertex data. TABLE 9 R = (a    ) R = (a +  d*e ) R = (a +b*c+  f) R = (a + b*c + d*e ) R = 1.0/(a    ) R = 1.0/(a +  d*e ) R =1.0/(a + b*c +  f) R = 1.0/(a + b*c + d*e )

[0155] As shown, there are four possibilities of products that might besummed in addition to an inverse operation (a, b*c, d*e, f, and 1/x).Next, mode fields might be defined. Table 10 illustrates a pair of modefields, mode.y and mode.z, each having assigned thereto a predeterminedset of the operations of Table 9. TABLE 10 mode.y[4] 0: R = a 1: R = a +d*e 2: R = a + b*c + f 3: R = a + b*c + d*e mode.z[2] 0: R = R 1: R =1.0/R

[0156] Thereafter, each of the operations might be positioned in memorywith an associated address. Table 11 illustrates a plurality of memoryaddresses each having an associated operation. Also shown is a set ofcontrol vector definitions. TABLE 11 ROM[0]: R = a ROM[1]: R = R + b*cROM[2]: R = R + d*e ROM[3]: R = R + f ROM[4]: R = 1.0/R cv[0] = 1; cv[1]= (mode.y==2 ∥ mode.y==3) ? 1 : 0; cv[2] = (mode.y==1 ∥ mode.y==3) ? 1 :0; cv[3] = (mode.y==2) ? 1 : 0; cv[4] = (mode.z==1) ? 1: 0;

[0157] Table 12 illustrates the execution of an example. TABLE 12 R =a+d*e corresponds to: mode.y = 1; mode.z = 0; which in turn affords thefollowing control vector: cv[0] = 1; cv[1] = 0; cv[2] = 1; cv[3] = 0;cv[4] = 0; execution first cycle: cv[0] is TRUE so execute ROM[0] moreTRUE values in control vector, so do not terminate program second cycle:cv[1] is FALSE so keep looking cv[2] is TRUE so execute ROM[2] no moreTRUE values in control vector, so terminate program

[0158] As such, sequencer 1200 of transform module 52 steps through athreaded control vector which is derived from threaded mode bits 202,and executes every ROM address whose corresponding control vector bit isset to “TRUE”. The control vector has the same length as the ROM. Thesequencer 1200 is capable of stepping through an arbitrary controlvector at the rate of one “1”, or enabled bit per a predetermined numberof cycles. Commands that do not use mode bits 202 might be executed byon-the-fly micro-code generation due to the simplicity thereof.

[0159] By representing such statuses by way of a unique string of modebits 202, it is unnecessary to execute a plurality of if-then clauses inthe graphics-processing hardware to determine the statuses of thevarious operations. Improved performance is thereby afforded.Conceptually, it is as if the if clauses in a program language had beenmoved to sequencer 1200 which in turn instantly skips instructions witha “FALSE” condition, as indicated by mode bits 202.

[0160] As indicated earlier, code segments are stored in the ROM whichare capable of handling the various statuses of the operationsidentified by the mode bits. In one embodiment a separate code segmentmight be retrieved for handling each operation indicated by the modebits. In the alternative, a single comprehensive code segment might bewritten for handling each or some combinations of operations that arepossible. It should be noted, however, that generating such large codesegments for each combination of operations requires additional codespace, and it therefore might be beneficial to modularize the codesegments for only commonly used combinations of operations.

[0161] Since mode bits 202 do not change once the vertex commencesexecution, the control vector generation might only have to be done onceper vertex before entering the sequencer. Exceptions to this might arisein some cases, however, such as lighting where operations might berepeated. When the last vertex instruction is found, an end of sequence(EOS) signal might be asserted. This in turn might be used to change thestatus of the input and output buffers, and to allow the start of thenext command in a manner that will be set forth during reference toFIGS. 28A and 28B. It should be noted that the EOS signal is pipelinedelayed for release of the destination buffer similar to the manner inwhich the instructions are handled. See FIG. 4B.

[0162]FIG. 14A is a flow diagram illustrating the various functionalcomponents of the present invention employed for integrating thehandling of scalar and vector vertex data during graphics-processing. Asshown, one functional aspect 1440 includes inputting vector vertex datainto a processing module, i.e. adder, multiplier, etc., for outputtingvector vertex data. In another functional aspect 1442, vector vertexdata is processed by a vector processing module, i.e. adder, multiplier,etc., which outputs scalar vertex data that is in turn converted, orsmeared, again into vector vertex data.

[0163] In yet another functional aspect 1444, vector vertex data ismasked, thereby converted to scalar vertex data, after which it isstored in memory, i.e. register logic unit, for the purpose ofgenerating vector vertex data. In still yet another functional aspect1446, scalar vertex data is extracted by a vector processing module,i.e. adder, multiplier, etc., which in turn is processed by a scalarprocessing module, i.e. inverse logic unit, which renders scalar vertexdata. This scalar vertex data is converted again into vector vertexdata.

[0164]FIG. 14B is a flow diagram illustrating one possible combination1451 of the functional components of the present invention shown in FIG.14A which corresponds to transform module 52 of FIG. 5. It should benoted that functional aspects 1444 and 1446 might have delays associatedtherewith in a manner similar to that set forth earlier during referenceto FIG. 4B. FIG. 14C is a flow diagram illustrating yet another possiblecombination 1453 of the functional components of the present inventionshown in FIG. 14A.

[0165] Multiplexers might accomplish the extraction of the scalar vertexdata from the vector vertex data in the functional modules of FIGS.14A-14C. Such multiplexers might also be responsible for any dataswizzling that might be required before processing by the variousfunctional modules. In one embodiment, the multiplexers might be capableof passing and rotating vector vertex data, and rely on othergraphics-processing modules such as an ALU for other processing. In yetanother embodiment, the multiplexers might be capable of arbitrarilyrearranging attributes independently without penalty.

[0166]FIG. 14D illustrates a method in which the transform system isadapted for performing a blending, or skinning operation duringgraphics-processing in a graphics pipeline via a hardware implementationsuch as an application specific integrated circuit (ASIC). Duringprocessing in the pipeline, in operation 1470, a plurality of matrices,a plurality of weight values each corresponding with one of thematrices, and vertex data are received. It should be noted that anadditional set of matrices might be required for normal vertex data.

[0167] Subsequently, in operation 1472, a sum of a plurality of productsis then calculated with each product being calculated by themultiplication of the vertex data, one of the matrices and the weightcorresponding to the matrix. Such sum of products is then outputted inoperation 1474 for additional processing.

[0168] In summary, the following sum of products might be calculated:

[0169] Equation #1

v′=Σw _(i) *M _(i) *v for i=1 . . .x

[0170] where

[0171] v=inputted vertex data

[0172] w=weight value

[0173] M=matrix

[0174] x=number of matrices

[0175] v′=vertex data for output to a processing module

[0176] Equation #2

n′=Σw _(i) *I _(i) *n for i=1. . .x

[0177] where

[0178] n=inputted vertex data (normal vector)

[0179] w=weight value

[0180] I=inverted matrix (inverse transpose matrix)

[0181] x=number of inverted matrices

[0182] n′=vertex data for output to a processing module (normal vector)

[0183] Equation #3

v_(s)=[O_(x), O_(y), O_(z), Ø]′+

1/(v′_(wc))*[(v′_(x)), (v′_(y)), (v′_(z)), 1]′

[0184] where v″=C*v′

[0185] v′=sum of products from Equation #1

[0186] C=[S_(x), S_(y), S_(z), 1]′* P

[0187] P=projection matrix

[0188] v_(s)=screen vector for display purposes

[0189] O=viewport offset

[0190] S=viewport scale

[0191] It should be noted that there are many ways to represent theweights w_(i) set forth hereinabove. For example, in Equations #1 and #2above, it might be said that i=1 . . . .(x−1), leaving w_(x) (w_(i)where i=x) to be calculated by the equation 1−Σw_(i.) By representingthe weights w_(i) in this way, it is ensured that all of the weights wsum to

[0192] In one embodiment, the matrices might include model view matrices(M), and the sum of products (v′) might be outputted for additionalprocessing by a lighting operation. See Equation #1. This sum ofproducts (v′) might also be used to generate another sum of products(v_(s)) for display purposes by using a composite matrix (C). SeeEquation #3. Still yet, the matrices might include inverse matrices (I)and the vertex data might include normal vector data (n). In such case,the additional processing might include a lighting operation. SeeEquation #2.

[0193]FIG. 15 is a schematic diagram of lighting module 54 in accordancewith one embodiment of the present invention. As shown, lighting module54 includes buffers 402 to which transform module 52 outputs the vertexdata. As shown, buffer 408 bypasses lighting module 54 by way of thepathway 1501. Further coupled to lighting module 54 is a context memory1500 and micro-code ROM memory 1502.

[0194] The lighting module 54 is adapted for handling lighting inaddition to fog and point parameters. In use lighting module 54 controlsthe buffer bypass pathway 1501, and calculates the diffuse, point size,and specular output colors as well as the fog value. It should be notedthat lighting module 54 employs the same mode bits 202 as transformmodule 52.

[0195] The lighting module 54 further requires less precision withrespect to transform module 52, and therefore processes 22 bit floatingpoint values (1.8.13 format) organized in tri-words. Since the data ofthird buffer 408 is 128 bits, it utilizes bypass pathway 1501 aroundlighting module 54. The lighting module 54 is event driven andsimultaneously executes three threads in a manner similar to transformmodule 52 as was set forth earlier with reference to FIGS. 4A and 4B. Itshould be noted that lighting module 54 might require command launchapproval from an outside source.

[0196]FIG. 16 is a schematic diagram showing the functional units oflighting module 54 of FIG. 15 in accordance with one embodiment of thepresent invention. As shown, included are input buffers 402 adapted forbeing coupled to a transform system for receiving vertex data therefrom.As set forth earlier, input buffers 402 include a first input buffer404, a second input 406, and a third input buffer 408. An input of firstbuffer 404, second input buffer 406, and third input buffer 408 arecoupled to an output of transform module 52. For bypass purposes, theoutput of third buffer 408 is coupled to the output of lighting module54 via a delay 1608.

[0197] Further included is a MLU 1610 having a first input coupled to anoutput of first input buffer 404 and a second input coupled to an outputof second input buffer 406. The output of MLU 1610 has a feedback loop1612 coupled to the second input thereof. An arithmetic logic unit (ALU)1614 has a first input coupled to an output of second input buffer 406.ALU 1614 further has a second input coupled to an output of MLU 1610. Anoutput of ALU 1614 is coupled to the output of lighting module 54. Itshould be noted that the output of ALU 1614 and the output of the thirdinput buffer 408 are coupled to the output of lighting module 54 by wayof multiplexer 1616.

[0198] Next provided is a first register unit 1618 having an inputcoupled to the output of ALU 1614 and an output coupled to the firstinput of ALU 1614. A second register unit 1620 has an input coupled tothe output of ALU 1614. Also, such second register 1620 has an outputcoupled to the first input and the second input of MLU 1610.

[0199] A lighting logic unit (LLU) 1622 is also provided having a firstinput coupled to the output of ALU 1614, a second input coupled to theoutput of the first input buffer 404, and an output coupled to the firstinput of MLU 1610. It should be noted that the second input of LLU 1622is coupled to the output of the first input buffer 404 via a delay 1624.Further, the output of LLU 1622 is coupled to the first input of MLU1610 via a first-in first-out register unit 1626. As shown in FIG. 16,the output of LLU 1622 is also coupled to the first input of MLU 1610via a conversion module 1628. In operation, such conversion module 1628is adapted for converting scalar vertex data to vector vertex data in amanner similar to that of transform module 52.

[0200] Finally, memory 1500 is coupled to at least one of the inputs ofMLU 1610 and the output of arithmetic logic unit 1614. In particular,memory 1610 has a read terminal coupled to the first and the secondinput of MLU 1610. Further, memory 1500 has a write terminal coupled tothe output of ALU 1614.

[0201] The memory has stored therein a plurality of constants andvariables for being used in conjunction with input buffers 402, MLU1610, ALU 1614, first register unit 1618, second register unit 1620, andLLU 1622 for processing the vertex data.

[0202]FIG. 17 is a schematic diagram of MLU 1610 of lighting module 54of FIG. 16 in accordance with one embodiment of the present invention.As shown, MLU 1610 of lighting module 54 includes three multipliers 1700in parallel. In operation, the present MLU 1610 is adapted to multiplytwo three component vectors, or pass one three component vector. Themultiplication of the three component vectors might be accomplished byway of a dot product or a parallel multiply. Table 13 illustrates theoperations that MLU 1610 of lighting module 54 is capable of performing.TABLE 13 ZMLU_MULT o[0] = a[0]*b[0], o[1] = a[1]*b[1], o[2] = a[2]*b[2]ZMLU_PASA o[0] = a[0], o[1] = a[1], o[2] = a[2] ZMLU_PASB o[0] = b[0],o[1] = b[1], o[2] = b[2]

[0203] Table 14 illustrates the possible A and B inputs of MLU 1610 oflighting module 54. TABLE 14 MA_V VBUFFER MA_L LLU MA_R RLU[2,3] (sharedwith MB_R) MA_C Context memory (shared with MB_C) MB_M MLU MB_W WBUFFERMB_R RLU[2,3] (shared with MA_R) MB_C Context memory (shared with MA_C)

[0204]FIG. 18 is a schematic diagram of ALU 1614 of lighting module 54of FIG. 16 in accordance with one embodiment of the present invention.As shown, ALU 1614 includes three adders 1800 in parallelseries. In useALU 1614 is capable of adding two three component vectors, or passingone three component vector. Table 15 illustrates the various operationsof which ALU 1614 of lighting module 54 is capable. TABLE 15 ZALU_ADDo[0] = a[0]+b[0], o[1] = a[1]+b[1], o[2] = a[2]+b[2] ZALU_SUM3B o[012] =b[0] + b[1] + b[2] ZALU_PASA o[0] = a[0], o[1] = a[1], o[2] = a[2]ZALU_PASB o[0] = b[0], o[1] = b[1], o[2] = b[2]

[0205] Table 16 illustrates the possible A and B inputs to ALU 1614 oflighting module 54. TABLE 16 AA_W WBUFFER AA_R RLU[0,1] AB_M MLU

[0206]FIG. 19 is a schematic diagram of register units 1618 and 1620 oflighting module 54 of FIG. 16 in accordance with one embodiment of thepresent invention. As shown, register units 1618 and 1620 each includetwo sets of registers 1900 each having an output connected to a firstinput of a corresponding multiplexer 1902 and an input coupled to asecond input of multiplexer 1902.

[0207] Register units 1618 and 1620 of lighting module 54 are split intotwo registers for ALU 1614 and two registers for MLU 1610. In oneembodiment, the registers are threaded. The register units 1618 and 1620exhibit zero latency when a write address is the same as a read addressdue to a bypass path from the input to the outputs.

[0208]FIG. 20 is a schematic diagram of LLU 1622 of lighting module 54of FIG. 16 in accordance with one embodiment of the present invention.LLU 1622 is the lighting unit of lighting module 54. It is a scalarblock that computes lighting coefficients later used to multiply thelight+material colors. LLU 1622 includes two MAC's, an inverter, foursmall memories, and a flag register.

[0209] The flag register is used to implement the conditional parts ofthe lighting equations. The outputs are an ambient, diffuse, andspecular coefficient. The scalar memories contain variables used for thespecular approximations and constants. The first location of each memorycontains 1.0 (for ctx0 and ctx2) and 0.0 (for ctx1 and ctx3). In oneembodiment, these are hardwired and do not need to be loaded.

[0210] In use LLU 1622 fundamentally implements the equation:(x+L)/(M*x+N). This equation is used to approximate a specular lightingterm. The inputs to LLU 1622 are from ALU 1614 of lighting module 54 andare the dot products used in the lighting equations. As set forthearlier, with respect to FIG. 16, there is an output FIFO 1626 betweenLLU 1622 and MLU 1610 which buffers coefficients until MLU 1610 needsthem. In one embodiment, such FIFO 1626 might be threaded along withdelays 1608 and 1624, and registers 1618 and 1620. Due to possible colormaterial processing, it is unknown when the diffuse and specular outputsare consumed by MLU 1610.

[0211] There is specially adapted hardware for dealing with the diffuseoutput alpha component since lighting module 54 only deals with R,G,Bcomponents. Such specially adapted hardware is capable of outputting twotypes of alpha components, namely vtx colorøα[Tbuffer], and stored ctxα[Ctx store]. The choice between the foregoing alpha components isgoverned by mode bits 202.

[0212] In operation, LLU 1622 calculates ambient (Ca), diffuse (Cde),and specular (Cs) coefficients of lighting. These coefficients are thenmultiplied with the ambient, diffuse, and specular colors to generate alight's contribution to the vertex color. Table 16A includes a list ofinputs received by LLU 1622 and the calculations carried out to generatethe ambient (Ca), diffuse (Cde), and specular (Cs) coefficients oflighting. It should be noted that any desired hardware configurationmight be employed to implement LLU 1622. In one embodiment, the specificconfiguration shown in FIG. 20 might be employed. TABLE 16A Inputdefinitions: n = normal vector (from transform engine) e = normalizedeye vector (from transform engine) l = normalized light vector (fromtransform engine) s = spotlight vector*light vector (from transformengine) D = distance vector (l,d,d*d) (from transform engine) h = halfangle vector (from lighting engine) K = attenuation constant vector(from context memory) (K0,K1,K2) The LLU might receive the followingscalar data in carrying out its calculations: n*l (from MLU/ALU) n*h(from MLU/ALU) K*D (from MLU/ALU) s (from transform engine) power0(material exponent from ctx0-3 memory) power1 (spotlight exponent fromctx0-3 memory) range (from ctx0-3 memory) cutoff (from ctx0-3 memory)Infinite Light LLU Calculations: Ca = 1.0 Cd = n*l Cs = (n*h){circumflexover ( )}power0 Local Light LLU Calculations: att = 1.0/(K*D) Ca = attCd = att*(n*l) Cs = att*((n*h){circumflex over ( )}power0) Spot LightLLU Calculations: att = (s{circumflex over ( )}power1)/(K*D) Ca = att Cd= att*(n*l) Cs = att*((n*h){circumflex over ( )}power0)

[0213] As set forth above, the mode bits controlling the vertexsequencer might not necessarily be changed by the vertex data itself orby any results derived from vertex data. To allow vertex data to modifyvertex processing, LLU 1622 employs a flag register 1623 is provided.Setting bits to TRUE in this flag register allows clamping to 0.0 ofcalculation results if a flag is specified in the output control of thecalculation. Another use of the flag register 1623 would be in setting awrite mask for register writes.

[0214] The flag register 1623 is provided in LLU 1622 for performing theif/then/else clamping to 0.0 in the lighting equations at no performancepenalty. The sign bit of various operands might set the flags. Table 16Billustrates the manner in which the flags in flag register 1623 are setand the resulting clamping. TABLE 16B Infinite Light LLU Calculations:Dflag = sign bit of(n*l) Sflag = sign bit of(n*h) Clamp: Ca = (0      )?0 : Ca; Cd(Dflag      )? 0 : Cd; Cs = (Dflag | Sflag) ? 0 : Cs; LocalLight LLU Calculations. Rflag = sign bit of (range-d) Dflag = sign bitof (n*l) Sflag =sign bit of (n*h) Clamp: Ca = (Rflag           )? 0 :Ca; Cd = (Rflag | Dflag       ) ? 0 : Cd; Cs = (Rflag | Dflag | Sflag) ?0 Cs; Spot Light LLU Calculations: Cflag = sign bit of(s-cutoff) Rflag =sign bit of (range-d) Dflag = sign bit of (n*l) Sflag = sign bit of(n*h) Clamp: Ca = (Cflag | Rflag          ) ? 0 : Ca; Cd = (Cflag |Rflag | Dflag        )? 0 : Cd; Cs = (Cflag | Rflag | Dflag | Sflag) ? 0: Cs;

[0215]FIG. 21 is an illustration of the organization of the flagregister 1623 associated with lighting module 54 of FIG. 16 inaccordance with one embodiment of the present invention. The flagregister 1623 contains 8 one bit flags and are set by the sign bit ofthe ALU (IFLAG) or MACO (MFLAG) outputs.

[0216] When LLU 1622 outputs a scalar value to MLU 1610 where it getssmeared into a tri-word, it specifies a mask for the flag register. Ifthe register & mask is true, 0.0 replaces the output. Table 17illustrates the various flags of FIG. 21 to be used in outputtingambient, diffuse, and specular attributes. TABLE 17 Ambient Mask: C, R,U Diffuse Mask: D, C, R, U Specular Mask: D, S, C, R, T, U

[0217] The approximation used for the specular term can go negativewhere the actual cos (theta)**n would go to 0.0. As a result, it isnecessary to perform a clamping operation. For this, the T, U flags areused. Table 18 illustrates various operations of which a functionallogic unit(FLU) 1621 of LLU 1622 is capable. Note FIG. 20. TABLE 18ZFLU_INV o = 1/a (mantissa accuracy - 12 bits) ZFLU_ISQ o = 1/sqrt(a)(mantissa accuracy - 6 bits) ZFLU_PASS o = a ZFLU_PASS1 o = 1.0ZFLU_MIN1 o = (a < 1.0) ? a:1.0 ZFLU_NOP o = 0.0

[0218]FIG. 22 is an illustration of the micro-code fields associatedwith lighting module 54 of FIG. 16 in accordance with one embodiment ofthe present invention. As shown, the micro-code of lighting module 54 isarranged into 33 fields making up a total width of 85 bits. Fields aredelayed to match the data flow of the units. The MLU operations are doneat a delay of zero, ALU operations are done at a delay of one, and RLU,LLU output operations are done at a delay of two. Each delay isequivalent to three cycles.

[0219]FIG. 23 is a schematic diagram of sequencer 2300 associated withlighting module 54 of FIG. 16 in accordance with one embodiment of thepresent invention. As shown, sequencer 2300 of lighting module 54includes an input buffer 2302 adapted for receiving mode bits 202 whichare indicative of the status of a plurality of modes of processoperations. Also included is memory 1502 capable of storing codesegments that each are adapted to carry out the process operations inaccordance with the status of the modes.

[0220] A sequencing module 2306 is coupled between memory 1502 andbuffer 2302 for identifying a plurality of addresses in memory 1502based on a control vector 2305 derived from the mode bits. Thesequencing module 2306 is further adapted for accessing the addresses inmemory 1502 for retrieving the code segments that might be used tooperate lighting module 54.

[0221] The sequencer 2300 of lighting module 54 is similar to that oftransform module 52. In operation, sequencer 2300 of lighting module 54steps through a threaded control vector that is derived from threadedmode bits 202 and executes every ROM address whose corresponding controlvector bit is set to “1”. The control vector has the same number of bitsas the ROM has words. The sequencer 2300 can step through an arbitrarycontrol vector at the rate of a single “1” or enabled bit per apredetermined number of cycles for every thread. Commands that do notuse mode bits 202 are executed by on-the-fly micro-code generation. Themain difference between sequencer 2300 of lighting module 54 andsequencer 1200 of transform module 52 is that sequencer 2300 of lightingmodule 54 can loop back and execute the lighting code up to eight times.

[0222] The sequencer 2300 of lighting module 54 has a light counter thatstarts at zero for each new vertex and increments by one at the end ofthe micro-code sequence. If the LIS field of mode bits 202 contains a“1” in the matching bit field, sequencer 2300 goes back and starts overat the beginning of the lighting micro-code block. This continues untila zero is found in the LIS field or eight lights have been done. Coloraccumulation is done by incrementing (per light) the ALU registers thatstore the diffuse and specular color. Automatic memory address indexingis done using the light counter to fetch the correct parameters for eachlight.

[0223]FIG. 24 is a flowchart delineating the method by which thesequencers of the transform and lighting modules 52 and 54 are capableof controlling the input and output of the associated buffers inaccordance with one embodiment of the present invention. As shown,vertex data is initially received in a buffer of a first set of buffersin operation 2420. The buffer in which the vertex data is received isbased on a round robin sequence.

[0224] Subsequently, in operation 2422, an empty buffer of a second setof buffers is identified also based on a round robin sequence. Thetransform module 52 is coupled between the first set of buffers and thesecond set of buffers. When the empty buffer of the second set ofbuffers is identified, the vertex data is processed in transform moduleand outputted from transform module to the identified empty buffer ofthe second set of buffers. Note operations 2424 and 2426.

[0225] Similarly, an empty buffer of a third set of buffers, or slots orspaces in memory, are identified based on a round robin sequence inoperation 2428. The lighting module 54 is coupled between the second setof buffers and the third set of buffers. When the empty buffer of thethird set of buffers is identified, the vertex data is processed in thelighting module, as indicated in operation 2430. The vertex data issubsequently outputted from lighting module 52 to the identified emptybuffer of the third set of buffers. See operation 2432. It should benoted that the number of buffers, or slots in memory, is flexible andmight be changed.

[0226]FIG. 25 is a diagram illustrating the method by which thesequencers of the transform and lighting modules 52 and 54 are capableof controlling the input and output of the associated buffers inaccordance with the method of FIG. 24. As shown, the first set ofbuffers, or input buffers 400, feed transform module 52 which in turnfeed the second set of buffers, or intermediate buffers 404, 406. Thesecond set of buffers 404, 406 feed lighting module 54 that drains tomemory 2550.

[0227] In order carry out the method set forth in FIG. 25, the slots ofmemory 2550 and the buffers of the first and second set are eachassigned a unique identifier upon initially receiving vertex data.Further, a current state of each buffer is tracked. Such state mightinclude an allocated state, a valid state, an active state, or a donestate.

[0228] The allocated state indicates that a buffer/slot is alreadyallocated to receive an output of the previous graphics-processingmodule, i.e. transform module or lighting module. When a write pointeris scanning the buffers/slots in the round robin sequence, a buffer/slotin the allocated state cause such write pointer to increment to the nextbuffer or slot.

[0229] If a buffer/slot is in the valid state, the buffer/slot isavailable for receiving vertex data. On the other hand, the active stateindicates that a buffer/slot is currently in an execution state, orreceiving vertex data. This active status is maintained until a threadis done after which a read pointer increments, thus placing thebuffer/slot back in the valid state. It should be noted that the firstset of buffers 400 are only capable of being in the valid state sincethere is no previous graphics-processing module to allocate them.

[0230] An example of a sequence of states will now be set forth. Uponreceiving vertex data in one of the first set of buffers 400 and a newset of command bits 200, such buffer is placed in the valid state, afterwhich one of the second set of buffers 402, 404 is placed in theallocated state in anticipation of the output of transform module 52.

[0231] If none of the second set of buffers 404, 406 is available forallocation, the vertex data in the buffer of the first set 400 can notbe processed. Further, a check might be done to determine whether thecode segments to be executed will interfere with any other code segmentsthat are to be simultaneously run. If so, the vertex data in the bufferof the first set 400 will not be processed and a stall conditioninitiated.

[0232] After one of the second set of buffers 404, 406 is placed in theallocated state, the buffer of the first set 400 is placed in the activestate. When transform module 52 is finished execution, the buffer of thesecond set 404, 406 is read and then placed in the valid state. Thesestate changes are similarly executed during the transfer of vertex databetween the second set 404, 406 and the slots of memory 2550.

[0233]FIG. 25B illustrates the rasterizer module 56 that comprises aset-up module 57 and a traversal module 58. The rasterizer module 56 isadapted for performing area-based rasterization in an alternatingmanner. In particular, a plurality of polygon-defining sense points arepositioned on or near the primitive after which line equations areevaluated at the points to determine which pixels reside in theprimitive. During operation, this evaluation is repeated as the pointsare moved in an alternating manner for efficiency purposes. Further, therasterizer module 56 might be adapted to operate without any clippingprocedure.

[0234]FIG. 26 illustrates a schematic of the set-up module 57 ofrasterization module 56. As shown, the set-up module 57 includes acontrol section 61 that handles routing data and control signals totheir appropriate functional units in order to perform the desiredfloating-point calculations. The primitive sequencer 62 handles turningsequences of vertices into triangles, lines or points. Further, floatingpoint data path section 64 includes the multiplexers and floating pointcomputation units that perform the math required in the set-up unit.

[0235] With continuing reference to FIG. 26, output formatting section63 handles converting the internal floating point format of edge slopesand edge values into integer formats suitable for the rasterizer sincethe rasterizer operates only with integer values. Of course, inalternate embodiments, the rasterizer might use a floating point thusobviating the need for output formatting section 63.

[0236] In operation, output formatting section 63 executes a blockfloating point conversion. As is well known, with a given number, i.e.2.34 e¹⁰, floating point format tracks a mantissa (2.34) and an exponent(10) thereof. Block floating point conversion essentially manipulatesthe decimal place of the mantissas of incoming data such that theexponents are the same. To this end, the exponent need not be handled inrasterizer module 56.

[0237]FIG. 26A is an illustration showing the various parameterscalculated by set-up module 57 of rasterizer module 56 of FIG. 25B. Suchparameters are required for rasterizer module 56 to perform theassociated functions. Upon receipt of a primitive 2600, set-up module 57calculates three values including slopes 2601 of the primitive 2600, astarting position 2602 and a starting value 2604.

[0238] The slopes 2601 are used to generate coefficients for lineequations of the edges of the primitive 2600 to be used duringrasterization. The slopes 2601 might, for example, be calculated byusing equations #4 and #5 shown below.

[0239] Equations #4 and #5

slope_(A)=y₀ −y ₁

slope_(B)=x₁ −x ₀

[0240] where y₀,y₁ and x₀,x₁ are coordinates of vertices shown in FIG.26A.

[0241] It should be noted that the slopes might also be calculated usingthe coordinates of the vertices by employing a simple rotation operationor the like.

[0242] The starting position 2602 indicates a starting point for arearasterization that will be set forth hereinafter in greater detail. Thestarting value 2604 is equal to the area of the shaded triangle shown inFIG. 26A and is also used during the area-based rasterization process.Such starting value 2604 is selected so that stepping the rasterposition about the screen while adding the slope at each step will equalzero exactly when the raster position is on the edge. Calculation of thestarting value 2604 might be accomplished using Equation #6 below:

[0243] Equation #6

starting_value=slope_(A)*(x _(s) −x ₀)+slope_(B)*(y _(s) −y ₀)

[0244] where

[0245] x_(s), y_(s)=starting position 2602

[0246] slope_(A), slope_(B)=slopes of one of the edges based oncoordinates of vertices shown in FIG. 26A

[0247] x₀,y₀=coordinates of one of the vertices of the edges shown inFIG. 26A

[0248] It should be understood that the foregoing values might also becalculated for other types of primitives. For example, in the case of aline, an extra slope must be calculated for the four-sided bounding box.Such slope can be easily calculated by taking the reciprocal of theslope of an opposite side of the bounding box. In addition to the extraslope calculation, it is noted that another starting value needs to becalculated in the case of the line primitive.

[0249]FIG. 27 illustrates the method by which rasterizer module 56handles one of a plurality of primitives, e.g. triangles. In particular,an initial operation is first performed by set-up module 57 ofrasterizer module 56. Upon receipt of a primitive, line equationcoefficients of line equations are determined for lines that define theprimitive in operation 2700 using slopes 2601 of FIG. 26A in a mannerthat is well known to those with ordinary skill in the art. As is wellknown, three line equations are required to define a triangle. On theother hand, a primitive such as a line is drawn as a rectangle orparallelogram with four sides and four line equations.

[0250] Thereafter, in operation 2702, the line equation coefficients aremodified if any primitive vertex(es) has a negative W-coordinate.Additional information regarding this process will be set forthhereinafter in greater detail with reference to FIG. 32.

[0251] It should be noted that set-up module 57 of rasterizer module 56also computes a bounding box of the primitive. For most triangles, thebounding box includes the minimum and maximum values of the threevertexes. For lines, the four parallelogram corners of the bounding boxare calculated. For triangles or lines that have a vertex with anegative W-coordinate, an area that is to be drawn extends beyond theconvex hull of the vertices.

[0252] One of the commands of OpenGL® is a scissor rectangle whichdefines a boundary outside of which is not to be drawn. The set-upmodule 57 of rasterizer module 56 calculates the intersection of thebounding box and the scissor rectangle. Since the scissor rectangle is arectangle, four additional line equations are afforded. It should benoted that the line equations associated with the scissor rectangle havea trivial form, i.e. horizontal or vertical.

[0253] Furthermore, in 3-D space, the near plane and far plane areparallel and at right angles to the line of sight. In the case of theprimitive being a triangle, three vertexes are included which define aplane that might have any orientation. The intersections of the plane ofthe primitive and the near and far planes include two lines with twoassociated line equations.

[0254] Accordingly, each primitive has a total of nine or ten lineequations depending on whether it takes the form of a triangle or aline, respectively. Again, in the case of the triangle, such lineequations include the three line equations which define the triangle,the four line equations defining the bounding box and the two lineequations which define the intersections of the plane in which theprimitive resides, and near and far planes.

[0255] With continuing reference to FIG. 27, the process progresses inoperation 2704 by positioning a plurality of points on or near theprimitive. The starting position 2602 dictates such positioning, asshown in FIG. 26A. Such points define an enclosed convex region andreside at corners of the convex region. FIG. 27A illustrates such sensepoints 2705 that enclose convex region 2707, e.g. a rectangle. In oneembodiment, such rectangle might be 8×2 pixels in size. Further, thepoints might be initially positioned to enclose a top vertex of theprimitive. As an option, this might be accomplished using truncation.

[0256] Once the primitive is positioned, the process is continued bytraversal module 58 which begins in operation 2706 by processing rows ofthe primitive in a manner set forth below. After the processing of eachrow, it is determined whether a jump position has been found in decision2708. A jump position is a starting position for processing the next rowand will be described hereinafter in greater detail. If it is determinedin decision 2708 that a jump position has been found, the sense pointsthat define the convex region are moved thereto in operation 2710. If,however, it is determined that a jump position has not been found, theprocess is ended. It should be noted that, in an alternate embodiment,columns, diagonals or any other type of string might be processed inoperation 2706 instead of rows.

[0257]FIG. 28 is a flowchart illustrating a process of the presentinvention associated with the process row operation 2706 of FIG. 27. Asshown, the process begins by computing the sense points in operation2800 in order to determine whether the polygon-defining sense pointsmight be moved right in decision 2801. Such decision is made based onthe position of the rightmost sense points. If the rightmost sensepoints are not positioned outside the same edge or edges of theprimitive, rightward movement is permitted and a position (X and Ycoordinates) to the right of the current position is stored as a snaplocation in operation 2802. If, however, both rightmost sense points arepositioned outside one or more edges of the primitive, rightwardmovement is not permitted and operation 2802 is skipped.

[0258] Next, the line equations are evaluated at the points of theconvex region, e.g. rectangle, in operation 2804. The evaluationincludes determining if the points reside in the primitive. Suchdetermination as to whether the points reside in the primitive mightinclude determining whether the evaluation of each of the line equationsrenders a positive value or a negative value at each of the sensepoints.

[0259] The line equations can be formulated to be positive inside theprimitive and negative outside. Inclusive edges, for which pixels thatlie exactly on the edge should be drawn, evaluate to zero and might betreated as positive. Exclusive edges, which should not be drawn, can bemade negative by initially subtracting a value of one from the startingline equation value. Thus pixels on exclusive edges evaluate to anegative value (−1) instead of a positive zero. This permits the sensepoint interpretation to ignore the inclusive/exclusive policy and justtest the line equation sign.

[0260] After the line equations are evaluated at the points, it isdetermined whether a current position of the sense points constitutes ajump position in decision 2806. It should be noted that a jump positionis stored only if the two bottom sense points are not both outside anedge. If it is determined in decision 2806 that a jump position has beenfound, the jump position is calculated and stored (or replaces apreviously stored jump position if existent) in operation 2808. If not,however, operation 2808 is skipped.

[0261] With continuing reference to FIG. 28, it is then determined indecision 2810 whether leftmost sense points are both outside an edge ofthe primitive. Again, this process entails determining whether theevaluation of the line equations at both of the leftmost sense pointsrenders positive or negative values. In particular, upon computation ofthe coefficients of the nine or ten edge equations at the pertinentsense points, nine or ten values are rendered that have nine or ten signbits. To determine if the current side is completely outside any edge,for example, the present invention AND's the ten sign bits from the twosense points together. If any bit(s) survive, then both points areoutside that edge.

[0262] If it is determined that the leftmost sense points are not bothoutside an edge of the primitive, it is concluded that there stillremains further portions of the primitive to be considered in theleftward direction, and the sense points are moved left in operation2812. If it is determined in decision 2810 that both leftmost sensepoints are indeed outside the edge of the primitive, it is concludedthat there no longer remains further portions of the primitive to beconsidered in the leftward direction. Next, in decision 2814, it isdetermined whether there is a snap location that resulted from operation2802.

[0263] If it is determined in decision 2814 that a snap location doesnot exist, the process is done. If, however, a snap location does exist,the sense points are moved to the snap location in operation 2816.Thereafter, operations similar to those of operations 2804-2812 areexecuted to map a right side of the primitive. This begins in operation2818 by the line equations being evaluated at the points of the convexregion.

[0264] After the line equations are evaluated at the points, it isdetermined whether a current position of the sense points constitutes ajump position in decision 2820. If it is determined in decision 2806that a jump position has been found, the jump position is calculated andstored in operation 2822. If not, however, operation 2822 is skipped.

[0265] With continuing reference to FIG. 28, it is then determined indecision 2824 whether rightmost sense points are both outside an edge ofthe primitive. If it is determined that the rightmost sense points arenot both outside an edge of the primitive, it is concluded that therestill remains further portions of the primitive in the rightwarddirection to be considered, and the sense points are moved right inoperation 2826. If it is determined in decision 2824 that both rightmostsense points are outside the edge of the primitive, it is concluded thatthere no longer remains further portions of the primitive to beconsidered in the rightward direction, and the instant process is done.

[0266]FIGS. 28A and 28B are illustrations of the sequence in which thesense points of the present invention might be moved about the primitive2850. It should be noted that various alterations might includedetermining whether the points can go left in decision 2800 andproceeding right initially. Further, the line equations might be definedto indicate whether the points are inside or outside the primitive inany desired way.

[0267] To avoid stepping in a repeating loop, the present invention thusemploys an overall direction of movement during rasterization. Theinitial implementation proceeds top-down, visiting every convex regionon a row before stepping down to the next. By processing rows top-downas well as never stepping right then left or left then right, loops arethus avoided.

[0268] An example of the foregoing process might be shown with referenceto the polygon-defining points, P1, P2, P3 and P4 of FIG. 27A. Inoperation, pairs of adjacent sense points can be examined to determinewhether stepping in their direction would be productive. For example, ifboth P3 and P4 in FIG. 27A were outside of an edge of a polygon, but P1and/or P2 are not, then clearly the drawable inside region lies to theleft, not to the right. Thus the sense points should not move right.Conversely, if both P3 and P4 are inside all the edges, then there is adrawable area just beyond P3 and P4, and stepping right is appropriate.Indeed, if P3 and P4 were not outside the same edge or edges, steppingright would be productive. This same logic applies to stepping upwardsguided by P1 and P3, or stepping left guided by P1 and P2, or steppingdownwards based on P2 and P4.

[0269] The foregoing process thus moves, or steps, the convex regiondefined by the points around the inside of the primitive, using sensepoints as a guide. Since the convex region defined by the points mightbe large, many pixels might be tested simultaneously. During use, if allsense points are inside all edges of the primitive, then all theenclosed pixels must be drawable (assuming a convex primitive). Asignificant advantage is afforded by testing the comers, namely theability of proving an arbitrary area of the primitive is inside, outsideor split. Only in the latter case do the individual pixels in the convexregion defined by the points need to be tested. In such case, the pixelsin the convex region defined by the points might be tested one-by-one orby another method in order to determine whether they reside in theprimitive. Furthermore, the sense points might reduce the amount offurther testing required by defining which edges(s) split the area andwhich do not.

[0270]FIG. 29 is a flowchart illustrating an alternate boustrophedonicprocess of the present invention associated with the process rowoperation 2706 of FIG. 27. As shown, it is first determined in decision2900 whether a previous movement was in a first or second direction. Ifthere was not any actual previous movement, a default previous movementmight be assumed. If it is determined in decision 2900 that the previousmovement was in a second direction, the line equations are evaluated atthe points of the convex region, e.g. a rectangle, in operation 2902 ina manner similar to operation 2804 of FIG. 28.

[0271] With continuing reference to FIG. 29, it is subsequentlydetermined in decision 2904 as to whether sense points of a first sideof the rectangle are both outside an edge of the primitive. If not, thesense points are moved or stepped in the first direction in operation2906. Upon it being determined that the sense points of the first sideof the rectangle are both outside an edge of the primitive, it is thendetermined in decision 2905 whether the points can be moved downwardlyor, in other words, whether the current position constitutes a jumpposition. If so, a jump position is calculated and stored in operation2908 after which the process is done.

[0272] On the other hand, if it is determined in decision 2900 that theprevious movement was in a first direction, operations similar to thoseof operation 2902-2908 are carried out. In particular, the lineequations are evaluated at the points of the convex region, e.g. arectangle, in operation 2910. It is then determined in decision 2912 asto whether sense points of a second side of the rectangle are bothoutside an edge of the primitive. If not, the sense points are moved orstepped in the second direction in operation 2914. Upon it beingdetermined that the sense points of the second side of the rectangle areboth outside an edge of the primitive, it is then determined in decision2913 whether the points can be moved downwardly or, in other words,whether the current position constitutes a jump position. If so, a jumpposition is calculated and stored in operation 2916 after which theprocess is done.

[0273]FIG. 29A is an illustration of the sequence in which the sensepoints of the present invention are moved about the primitive inaccordance with the boustrophedonic process of FIG. 29. The foregoingboustrophedonic rasterization constrains the sequence to obey certainrules that offer better performance for hardware. As shown, theboustrophedonic rasterization affords a serpentine pattern that foldsback and forth. A horizontal boustrophedonic sequence, for example,might generate all the pixels within a primitive triangle that are onone row from left to right, and then generate the next row right toleft, and so on. Such a folded path ensures that an average distancefrom a generated pixel to recently previously generated pixels isrelatively small.

[0274] Generating pixels that are near recently previously generatedpixels is important when recent groups of pixels and/or theircorresponding texture values are kept in memories of a limited size. Theboustrophedonic sequence more often finds the pixels or texture valuesalready loaded into such memories, and therefore repeating the memoryload occurs less often.

[0275] As an option, at least one boundary might be used which dividesthe primitive into a plurality of portions prior to rasterization. Inoperation, the points might be moved in each of the portions separately.Further, the points might be moved through an entirety of a first one ofthe portions before being moved in a second one of the portions.

[0276]FIG. 30 is a flowchart illustrating an alternate boustrophedonicprocess using boundaries. As an option, the decision whether to useboundaries might be based on a size of the primitive. As shown in FIG.30, the boustrophedonic process which handles boundaries is similar tothat of FIG. 27 with the exception of an additional operation 3000wherein at least one boundary is defined which divides the primitiveinto a plurality of portions or swaths.

[0277] With continuing reference to FIG. 30, an additional decision 3001follows the completion of every portion of the primitive. In particular,it is determined in decision 3001 whether a start position of anadjacent portion was found in operation 3006. If so, the convex regiondefined by the sense points is moved to a start position of an adjacentportion of the primitive in operation 3002 and operations 3004-3010 arerepeated for the new portion of the primitive. Further informationrelating to the determination of the start position in operation 3006will be set forth in greater detail during reference to FIG. 31.

[0278]FIG. 31A is an illustration of the process by which the convexregion of the present invention is moved about the primitive inaccordance with the boundary-based boustrophedonic process of FIG. 30.As shown, the first portion that is processed is that which includes thetopmost vertex of the primitive. During operation, a left neighboringportion is processed after which the adjacent left neighboring portionis processed and so on. This is continued until there are no remainingleft neighboring portions. Next, a neighboring portion to the right ofthe first portion is processed after which the adjacent rightneighboring portion is processed and so on until all of the rightneighboring portions are processed. It should be appreciated that othertypes of ordering schemes might be utilized per the desires of the user.

[0279]FIG. 31 is a flowchart showing the process associated with theprocess row operation 3006 of FIG. 30. Such process is similar to theboustrophedonic process of FIG. 29 with the exception of decisions 3118through 3121. Decisions 3118 and 3120 both determine whether any of thesense points have passed any boundary. Only if it is determined that thesense points are still within the boundaries is the respective loopcontinued.

[0280] In operations 3119 and 3121, starting positions of adjacentportions of the primitive are sought and stored when it is determined indecisions 3118 and 3120 that any sense points of the convex region havepassed any boundary, respectively. As shown in FIG. 31A, such startingpositions 3126 are each defined as being the topmost point of a portionof the primitive existent beyond a boundary. By storing this position, astarting point is provided when the process is repeated for the adjacentboundary-defined portion of the primitive.

[0281] It should be noted that operations 3119 and 3121 are bothperformed while processing the first portion of the primitive. While notexpressly shown in FIG. 31, only a first one of such operations isperformed when processing portions to the left of the first portion,while only a second one of such operation is performed when processingportions to the right of the first portion. In other words, whenprocessing portions to the left of the first portion, starting positionsare only determined when a leftmost boundary of the currently processedportion has been exceeded. Similarly, when processing portions to theright of the first portion, starting positions are only determined whena rightmost boundary of the currently processed portion has beenexceeded.

[0282] Using boundaries during rasterization solves a very criticalproblem during pipeline processing. If a primitive is very wide, thestorage associated with the pixels of a single row might not fit in alimited-size memory. Rasterization with boundaries divides the triangleinto limited-width rows (or columns), and generates all the pixelswithin such a portion before moving on to the next portion.

[0283] For example, even if a triangle is 100 pixels wide, alimited-size pixel or texture memory might only hold information for theprevious 20 pixels. Constraining the pixel sequence to stay withinten-pixel-wide vertical portions allows all the pixels on the previousand current rows to fit in the memory. This means that a boustrophedonicsequence within a boundary-defined portion would always have theprevious pixel on the current row (if any) in the memory, as well as thepixels in the row above (if any) in the memory as well.

[0284] Most underlying memory systems transfer blocks of data with acertain overhead per block. Small accesses to the memory system arepenalized heavily by this overhead. In order to be efficient, largeraccesses are employed and the rest of the block is maintained in case itmight be used next. Beyond that, a cache memory system keeps a pluralityof these recent blocks, increasing the probability that memory accessescan be avoided.

[0285] The boustrophedonic sequence of the present invention exploitsthe single-retained-block concept when it reverses and handles pixelsimmediately below one end of the current line. Further, theboustrophedonic sequence exploits cache when it limits rasterization toportions of a particular size. Specifically, two scanlines within aportion should fit in the cache, so throughout the second scanline,benefits might be incurred from cache storage of the first scanline.

[0286] There is no constraint on the sequence or number ofboundary-defined portions. Although the present description uses theexample of vertical portions and a horizontal boustrophedonic pattern,similar principles might extend to horizontal portions, verticalboustrophedonic patterns or even to diagonal portions and patterns. Inone embodiment, the length of the strings (e.g. rows, columns,diagonals, etc.) might be each limited to be less than a dimension ofthe primitive along which the string resides.

[0287]FIG. 32 is a flowchart showing the process associated withoperation 2702 of FIG. 27. The instant process is designed to handle aprimitive with portions that reside behind the eye. These outlyingportions might cause problems in subsequent rasterization operations. Toaccomplish this, the instant process employs a variable, W that iscommonly used for projection i.e., for viewing objects in perspective.The variable W is a number that the other coordinates, X, Y and Z, aredivided by in order to make nearby things larger and far things smaller.The variable W is representative of a distance between a center ofprojection and the corresponding vertex.

[0288] As shown in FIG. 32, a primitive is first received that isdefined by a plurality of vertices. Each of such vertices includes aW-value. Upon the receipt of the primitive, the set-up module serves todefine lines that characterize the primitive based on the vertices. Noteoperation 3200.

[0289] The W-values are then analyzed in decision 3202. As shown, if oneof the W-values is negative, a line equation for a line opposite thevertex having the negative value is flipped in operation 3204. In otherwords, the coefficients of the line equation are multiplied by −1.Further, if two of the W-values are negative, line equations for linesconnecting the vertex having a positive W-value and each of the vertexeshaving negative W-values are flipped in operation 3206. If three of theW-values are negative, a cull condition 3207 occurs where the presentinvention culls the triangle. Still yet, if none of the W-values arenegative, no additional action is taken.

[0290] FIGS. 32A-32C illustrate the manner in which flipping lineequations affects which portion of the screen is processed. FIG. 32Ashows the case where none of the W-values are negative and the lineequations are left unaltered. As shown, an interior portion of theprimitive is filled in such case.

[0291]FIG. 32B shows the case where one of the W-values is negative andwhich of the line equations is flipped accordingly. As shown, theportion of the primitive opposite the vertex is filled in the presentcase. In particular, the area to be drawn is bounded by two lines thatare co-linear with the two triangle sides sharing the −W vertex, andfurther bounded by a side of the triangle that shares the two +Wvertexes.

[0292]FIG. 32C shows the case where two of the W-values are negative andwhich of the line equations are flipped accordingly. As shown, theportion of the primitive opposite the vertexes is filled using themethods and/or processes set forth hereinabove with reference to FIGS.27-32. In other words, the area to be drawn is bounded by two lines thatare co-linear with the two triangle sides sharing the +W vertex, andfurther contiguous to the +W vertex.

[0293] The present invention is thus capable of handling all three ofthe foregoing cases. If part of the triangle is beyond the near and/orfar plane, it draws only the portion within those planes. If thetriangle has one or two negative Z vertexes, only the correct +Z portionis drawn.

[0294] Even if all vertexes are off-screen, and the triangle extendsfrom behind the eye to beyond the far plane, whatever pixels are insidethe triangle and on the screen and have Z between the near and farlimits. The present invention ensures that little time is wastedexploring bad pixels. This is possible because all clipping, by screenedge or the near or far plane, always results in a convex regionon-screen which can be explored easily.

[0295] A problem sometimes arises when the starting point is not insidethe area to be filled. This can occur if the top vertex is off-screen oris clipped by the near or far plane. In this case, the traversal stagemust search for the top point of the drawn region, starting from above.It can do this efficiently by being guided by the signs of the triangleedge slopes and the Z slope. It can test the triangle line equations todiscover it is outside the drawn region and why. When it knows whatedge(s) and/or Z limit it is outside of, it knows what direction(s) tostep that brings it closer to that edge or limit. By moving horizontallyin preference to vertically (when there is a choice), searching for thedrawn region guarantees it finds the top drawable pixel if there is one.This problem also occurs with external (−W) triangles that open up. Inthis case, the drawn area extends above all three vertexes.

[0296] In one embodiment of the present invention, traversal proceedsfrom top to bottom of the triangle. The starting point is the top vertexof the triangle if none have a negative W-value and the top vertex is inthe scissor rectangle. Otherwise, a point on the top of the scissorrectangle is chosen. Since traversal always begins within the scissorrectangle and never ventures out of it, only the portion of the trianglewithin the scissor rectangle is ever drawn, even if the area enclosed bythe edges extends far beyond the scissor rectangle. In this way, simplescissor rectangle-edge clipping is effected.

[0297] While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A graphics pipeline system for graphicsprocessing, comprising: (a) a transform module adapted for being coupledto a buffer to receive vertex data therefrom, the transform module beingpositioned on a single semiconductor platform for transforming thevertex data from object space to screen space; (b) a lighting modulecoupled to the transform module and positioned on the same singlesemiconductor platform as the transform module for performing lightingoperations on the vertex data received from the transform module; and(c) a rasterizer coupled to the lighting module and positioned on thesame single semiconductor platform as the transform module and lightingmodule for rendering the vertex data received from the lighting module.2. The system as recited in claim 1, wherein the lighting moduleincludes: (a) a plurality of input buffers adapted for receiving thevertex data; (b) a multiplication logic unit having a first inputcoupled to an output of one of the input buffers and a second inputcoupled to an output of one of the input buffers; (c) an arithmeticlogic unit having a first input coupled to an output of one of the inputbuffers and a second input coupled to an output of the multiplicationlogic unit; (d) a first register unit having an input coupled to theoutput of the arithmetic logic unit and an output coupled to the firstinput of the arithmetic logic unit; (e) a second register unit having aninput coupled to the output of the arithmetic logic unit and an outputcoupled to the first input and the second input of the multiplicationlogic unit; (f) a lighting logic unit having a first input coupled tothe output of the arithmetic logic unit, a second input coupled to theoutput of one of the input buffers, and an output coupled to the firstinput of the multiplication logic unit; and (g) a memory coupled to atleast one of the inputs of the multiplication logic unit and the outputof the arithmetic logic unit.
 3. The system as recited in claim 2,wherein an output of one of the input buffers is coupled to an output ofthe lighting module via a delay.
 4. The system as recited in claim 3,wherein the output of the arithmetic logic unit and an output of one ofthe input buffers are coupled to the output of the lighting module byway of a multiplexer.
 5. The system as recited in claim 2, wherein theoutput of the multiplication logic unit has a feedback loop coupled tothe second input thereof.
 6. The system as recited in claim 2, whereinthe second input of the lighting logic unit is coupled to an output ofone of the input buffers via a delay.
 7. The system as recited in claim2, wherein the output of the lighting logic unit is coupled to the firstinput of the multiplication logic unit via a first-in first-out registerunit.
 8. The system as recited in claim 2, wherein the output of thelighting logic unit is coupled to the first input of the multiplicationlogic unit via a conversion module adapted for converting scalar vertexdata to vector vertex data.
 9. The system as recited in claim 1, whereinthe transform module includes: (a) an input buffer adapted for receivingvertex data; (b) a multiplication logic unit having a first inputcoupled to an output of the input buffer; (c) an arithmetic logic unithaving a first input coupled to an output of the multiplication logicunit; (d) a register unit having an input coupled to an output of thearithmetic logic unit; (e) an inverse logic unit including an inputcoupled to the output of the arithmetic logic unit or the register unitfor performing an inverse or an inverse square root operation; (f) aconversion module coupled between an output of the inverse logic unitand a second input of the multiplication logic unit, the conversionmodule adapted to convert scalar vertex data to vector vertex data; and(g) a memory coupled to the multiplication logic unit and the arithmeticlogic unit.
 10. The system as recited in claim 9, wherein the memory iscoupled to the second input of the multiplication logic unit.
 11. Thesystem as recited in claim 9, wherein the memory has a write terminalcoupled to the output of the arithmetic logic unit.
 12. The system asrecited in claim 9, wherein the output of the multiplication logic unithas a feedback loop coupled to the first input thereof.
 13. The systemas recited in claim 9, wherein the output of the register unit iscoupled to the first input of the multiplication logic unit.
 14. Thesystem as recited in claim 13, wherein the output of the register unitis coupled to the second input of the multiplication logic unit.
 15. Thesystem as recited in claim 9, wherein the output of the arithmetic logicunit has a feedback loop connected to the second input thereof.
 16. Thesystem as recited in claim 15, wherein the feedback loop has a delaycoupled thereto.
 17. The system as recited in claim 1, wherein therasterizer operates in homogeneous clip space.
 18. The system as recitedin claim 1, wherein the rasterizer is adapted for receiving a primitivedefined by a plurality of vertices each including a W-value; andidentifying an area based on the W-values, wherein the area isrepresentative of a portion of a display to be drawn corresponding tothe primitive.
 19. A graphics pipeline system for graphics processing,comprising: (a) transform means adapted for being coupled to a buffer toreceive vertex data therefrom, the transform means positioned on asingle semiconductor platform for transforming the vertex data fromobject space to screen space; (c) lighting means positioned on the samesingle semiconductor platform as the transform means for performinglighting operations on the vertex data received from the transformmeans; and (d) rasterizer means positioned on the same singlesemiconductor platform as the transform means and lighting means forrendering the vertex data received from the lighting means.
 20. A methodfor graphics processing, comprising: (a) transforming vertex data fromobject space to screen space; (b) lighting the vertex data; and (c)rendering the vertex data, wherein the vertex data is transformed,lighted, and rendered on a single semiconductor platform.
 21. The methodas recited in claim 20, wherein prior to rendering, the graphicsprocessing further comprises: receiving a primitive defined by aplurality of vertices each including a W-value; and identifying an areabased on the W-values, wherein the area is representative of a portionof a display to be drawn corresponding to the primitive.
 22. A graphicspipeline system for graphics processing, comprising: (a) a lightingmodule adapted for being coupled to a transform module to receive vertexdata therefrom, the lighting module being positioned on a singlesemiconductor platform for performing lighting operations on the vertexdata received from the transform module; and (b) a rasterizer coupled tothe lighting module and positioned on the same single semiconductorplatform as the lighting module for rendering the vertex data receivedfrom the lighting module.
 23. A method for graphics processing,comprising: (a) lighting vertex data; and (b) rendering the vertex data,wherein the vertex data is lighted and rendered on a singlesemiconductor platform.
 24. A graphics pipeline system for graphicsprocessing, comprising: (a) a transform module adapted for being coupledto a buffer to receive vertex data therefrom, the transform module beingpositioned on a single semiconductor platform for transforming thevertex data from object space to screen space; and (b) a rasterizerpositioned on the same single semiconductor platform as the transformmodule for rendering the vertex data.
 25. A method for graphicsprocessing, comprising: (a) transforming vertex data from object spaceto screen space; and (b) rendering the vertex data, wherein the vertexdata is transformed and rendered on a single semiconductor platform.